The author of al Durr al Mukhtaar, explaining the Hanafi position says: 'For men the hands should be below the navel.'
Imam Malik رحمه الله has three narrations: 1) Not fastening the hands at all but letting them hang at the sides. This is the most famous ruling of his madhab. 2) A choice of fastening or letting them hang at the sides. 3) Placing the hands above the navel but below the chest.
Imam Shafiee رحمه الله says that they should be placed above the navel but below the chest. Imam Nawawi رحمه الله discusses this in his commentary of Muslim saying, 'This is the better known ruling of our Madhab.' He also says in Sharh al Muhaddhab, 'He should place them below his chest and above his navel. This is the correct and clear ruling (of our school).'
Imam Shafiee رحمه الله also has two other narrations but they are not well known: below the navel and on the chest.
Imam Ahmed Ibn Hanbal's رحمه الله view is that that hands should be fastened below the navel. This is his most famous narration and is adopted by virtually all the hanbali ulama.
Ibn al Qayyim رحمه الله writes in his Badai' al Fawaid that Abu Talib رحمه الله said, 'I asked Ahmed Ibn Hanbal رحمه الله, 'Where should a man place his hands when praying?' He replied, 'Upon the navel or below it.'' [Badai' al Fawaid 3/73]
Tha Hanbali scholar of 18th century Arabia, Sheikh Muhammad Ibn 'Abdul Wahhab رحمه الله also says, 'He should then clasp his left wristbone with his right hand and place them below the navel. This signifies humbleness before his Lord, the Almighty.' [Kitab Adaab al Mashy ila al Salah, second section on fiqh, p6]
Sheikh ul Hadeeth Moulana Muhammad Zakariyya رحمه الله quotes the authors of Nail al Maarib, al Anwaar and al Rawdh al Murabb'a in his Awjaz al Masalik and then concludes, 'We learn from this that the preferred and secure narration amongst the Hanbali ulama is that of below the navel.' [Awjaz al Masalik 3/171]
The Hanbali scholar Alaa al Deen al Mardawi رحمه الله writes in his al Insaaf, 'He should place his hands below the navel. This is the Madhhab (of the Hanbali's), and upon this are the clear majority of the Hanbali ulama.' [al Insaaf 1/46]
Imam Ahmed رحمه الله also has two other narrations:
1) Above the navel but below the chest.
2)A choice of either of the two positions without preference for either.
The Opinion of all the Imams and 'Ulama can therefore be summarised into three positions
1) Above the navel but below the chest.
2) Below the navel.
3) Not fastening the hands at all, but letting them hang at the sides.
Thus, in reality, there are only two positions of fastening the hands: above the navel, and below it. No school of fiqh advocates the fastening of the hands on the chest.
Abu al tayyib al Madani رحمه الله writes in his commentary on Tirmidhi that none of the four Imams adopted the practise of placing the hands on the chest.
Ibn al Qayyim al Jawziyyah رحمه الله also writes in his Badai' al Fawaid, 'It is makrooh (undesirable) to place the hands on the chest in view of the narration that the Prophet (sallallahu alaihi wa sallam) forbade takfeer, which is to place the hands on the chest.' (Bada'i al Fawa'id, 3/73)
1. Sayyiduna Wail Ibn Hujr رضي الله عنه says, 'I prayed with the Prophet صلى الله عليه وسلم and he placed his right hand over his left on his chest. (Ibn Khuzaimah, 479)
Imam Nimawi رحمه الله says, 'It's isnad is questionable and the additional wording 'on his chest' is inauthentic and not established.'
This hadeeth has been reported by Muammal Ibn Ismaeel رحمه الله from Sufyan ath-Thawri رحمه الله from Aasim Ibn Kulaib رحمه الله from Wail bin Hujr رضي الله عنه -However it is only Muammal who reports these additional words from Sufyan ath-Thawri رحمه الله. Sufyan's رحمه الله other student, Abdullah Ibn al Waleed رحمه الله who also narrates this hadeeth from him does not include these words in his narration as recorded in Imam Ahmad's Musnad. (Ahmad 18392)
The other narrators who report the hadeeth together with Sufyan ath-Thawri رحمه الله from Aasim bin Kulaib رحمه الله have also not included these words in their narrations. Observe the following list of narrators who have al reported the same hadeeth from Aasim bin Kulaib رحمه الله but none of then have included the additional words reported by Muammal bin Ismaeel رحمه الله
• Sh'ubah, Abdul Wahid, and Zubair bin Muawiyah as in Imam Ahmad's Musnad. (Ahmad 18398, 18371 & 18397)
• Zaidah as in Imam Ahmad's Musnad, Darimi, Abu Dawood. Nasai and Baihaqi (Ahmad 18391, Darimi 1357, Abu Dawood 726, Nasai 889 and Baihaqi 2325)
• Bishr bin al Mufaddhal as in Ibn Majah, Abu Dawood and Nasai (Ibn Majah 810, Abu Dawood 726 & 957, and Nasai 1265)
• Abdullah bin Idrees as in Ibn Majah (Ibn Majah 810)
• Salam bin Saleem as in Abu Dawood Tayalisi's Musnad (Abu Dawood Tayalisi 1020)
There are many other chains for this hadeeth, however, none contain this extra wording. Thus, it is clear that this is Muammal bin Ismaeel's own erroneous addition to the hadeeth. Ibn al Qayyim al Jawziyyah رحمه الله also says in I'laam al Muwaqqieen, 'No one has said upon the chest apart from Muammal bin Ismaeel.’ (I'ilaam al Muwaqqieen 2/361) Therefore, as Imam Nimawi رحمه الله has concluded in his al Ta'leeq al Hasan, this hadeeth with the additional wording of' upon his chest' is extremely weak.
It is an accepted principle of hadeeth that if a certain authentic and reliable narrator contradicts other equally authentic or more reliable 'arrators in his wording of a hadeeth then his narration will be declared shaadh and will not be accepted. If this is the case with authentic narrators, then an irregular addition of the words 'upon the chest' cannot be accepted from a narrator who, although declared acceptable by some, errs excessively and is weak of memory like Muammal bin Ismaeel. Study the following observations of the scholars of Jarh and T'adeel about Muammal bin Ismaeel:
Abu Hatim رحمه الله says, 'He is sadooq, firm in sunnah, but one of many mistakes'
lmaam Dhahabi رحمه الله states in Al-Mizan (on the Authority of Imam Bukhari رحمه الله): “His hadith are disowned.”
(People who view Imam Bukhari رحمه الله as the ultimate authority in matters of Hadeeth should note his following statement: 'It is not permissible to narrate from anyone whom I have labelled munkar al hadeeth.'
Dhahabi رحمه الله says in al Kashif, 'He is sadooq, firm in sunnah, but one of many mistakes. It was also said that he buried his books and narrated by heart and thus erred. '
Ibn Sa'd رحمه الله says, 'He is thiqah, though one of many mistakes.'
Yakub bin Sufyan رحمه الله says, 'Muammal Abu Abdul Rahman is a great sunni shaikh. I heard Sulaiman bin Harb praise him. Our shaikhs would advise us to take his hadeeth, only that his hadeeth are not like the hadeeth of his companions. At times it is obligatory upon the people of knowledge to distance themselves from his narrations as he narrates munkar ahadeeth from even his authentic teachers. This is worse for had he narrated these munkar ahadeeth from weak authorities we would have excused him.'
Saji رحمه الله says, 'He errs excessively. He is sadooq, but one of many mistakes. He has errors that would take too long to be mentioned.'
Muhammad bin Nasr al Marwazi رحمه الله says, 'If Muammal alone relates a certain narration then it becomes obligatory to pause and research the hadeeth as he had a bad memory and erred excessively' (See Tahdheeb al Tahdheeb)
Hafidh Ibn Hajar رحمه الله has made it clear in his Fath al Bari that there is dh'af (weakness) in Muammal bin Ismaeel's narrations from Sufyan (Fath al Bari, 9/297). The above hadeeth has this very chain of narration.
We must also bear in mind that Sayyiduna Wail Ibn Hujr رضي الله عنه, the very companion who narrates this hadeeth, was a resident of Kufa, and the practice of the people of Kufa was to fasten their hands below the navel. There is nothing to suggest that he contravened this practice. Sufyan ath-Thawri رحمه الله, from whom Muammal narrates this hadeeth, is himself of the view that the hands should be placed below the navel (Ibn Qudamah رحمه الله in al Mughni 2/23, and others as quoted by the author of Bughyah al Almaee 1/316)
Furthermore, there is another hadeeth narrated by Sayyiduna Wail (ra) himself (quoted above) which says that he saw the Prophet صلى الله عليه وسلم fasten his hands below the navel.
2. Sayyiduna Hulb رضي الله عنه relates, 'I saw the Prophet صلى الله عليه وسلم turn from both his right and left and I also saw him place this upon his chest.' Yahya (one of the narrators) described this as being the right hand upon the left above the wrist joint. 
The above hadeeth contains the words 'upon his chest'. This extra wording is not firmly established or confirmed, because of all the narrators who report this hadeeth from Simak, only one reports this extra wording.
Observe the following narrations of the same hadeeth without the extra wording of 'upon his chest'.
• Abu al Ahwas رحمه الله reports from Simak bin Harb رحمه الله from Qabeesah bin Hulb رحمه الله from his father that the Prophet (sallallahu alaihi wa sallam) would lead us in prayer and would clasp his left hand with his right. 
• Shareek رحمه الله reports from Simak رحمه الله from Qabeesah bin Hulb رحمه الله from his father who says (towards the end of a longer hadeeth), 'I saw him place one of his hands on the other and I also saw him turn once towards his right and once towards his left.' 
Wakee' رحمه الله reports from Sufyan رحمه الله from Simak bin Harb رحمه الله from Qabeesah bin Hulb رحمه الله from his father who says, 'I saw the Prophet صلى الله عليه وسلم place his right hand upon his left in prayer and I also saw him turn away from both his right and left.' 
• Daruqutni رحمه الله narrates from Abdul Rahman bin Mahdi رحمه الله and Wakee' رحمه الله, from Sufyan رحمه الله from Simak bin Harb رحمه الله from Qabeesah bin Hulb رحمه الله from his father who says, 'I saw the Prophet صلى الله عليه وسلم place his right hand upon his left in prayer.' (Daruqutni 1087)
The above narrations all clearly show that the wording 'upon his chest' is an unreliable addition on the part of one of the reporters and therefore this particular narration is shaadh.
Imam Nimawi رحمه الله adds in his al T'aleeq al Hasan (1/145):
'I have a suspicion that the wording of this hadeeth has mistakenly been changed by a writer. The correct words would appear to be "Yadhau hadhihi ala hadhihi", i.e., "he would place this hand upon this hand", and not "hadhihi ala sadrihi", i.e., "this hand upon his chest". Only this wording would be in agreement with the narrators own interpretation of the hadeeth as is stated in the narration "Yahya described this as being the right hand upon the left above the wrist joint". This would also tally with all the other narrations of this hadeeth that do not contain the wording "upon the chest", and would also explain why the following authors have not included this narration in their comprehensive books: Haithami in his Majm'a al Zawaid, Suyuti in his Jam' al Jawami, and Ali al Muttaqi in his Kanz alUmmal. And Allah knows best.'
The author of Awn al M'abud also admits that Yahya's commentary does not fit the wording of the hadeeth.
3. Taawoos رحمه الله narrates that The Messenger of Allah صلى الله عليه وسلم used to place his right hand over his left, and then clasp them firmly on his chest during prayer. [Abu Dawood 759]
Imam Nimawi رحمه الله has declared this hadeeth to be weak. 
This hadith is mursal and its isnad contains Sulaiman bin Musa رحمه الله who has been classified as weak by some scholars. Bukhari رحمه الله claims that he has munkar narrations. Nasa'i رحمه الله says that he is not strong in Hadeeth. Hafidh رحمه الله says in al Taqreeb, “He is a sadooq and faqeeh. There is some (leen) “weakness” in his hadeeth.” Furthermore, Abu Dawood رحمه الله has recorded the same narration in his Maraseel but with a different wording. Instead of “he clasped them firmly on his chest” that narration reads “he entwined the fingers of his hands on his chest. [Maraseel Abi Dawood, p85]
This hadeeth is also mursal and although mursal narrations are not readily accepted by others, the Hanafi Ulama consider them acceptable as evidence. Therefore, as some have pointed out, this narration is binding on us. However, we say that the saheeh hadith of Sayyiduna Wail bin Hujr [radiyallahu anhu] narrated by Ibn Abi Shaibah رحمه الله takes precedence and the ahadeeth of Sayyidina Ali (ra) and Sayyiduna Abu Hurairah (ra) are more acceptable to us because they explicitly mention the sunnah being below the navel. Tawoos’s words “he would” cannot match the words of the companions “it is sunnah”. Also as mentioned earlier the very wording of Tawoos’s hadeeth is in dispute. Moreover, Tawoos’s mursal narration is opposed to the mursal narrations of Ibrahim al Nakhai and Abu Mijlaz.
Imam Nimawi رحمه الله writes in Aathaar as-Sunan that there are other ahadeeth about placing the hands on the chest but they are all weak. Of these he mentions the following:
4. Sayyiduna Wail ibn Hujr رضي الله عنه narrates, “I was present with the Prophet صلى الله عليه وسلم. He rose, went towards the masjid and entered the mihraab. He raised his hands with takbeer and then placed his right hand over his left upon his chest.” [Bayhaqi 2335]
Imam Nimawi رحمه الله says, "Its isnad is extremely weak. Dhahabi has said about Muhammad bin Hujr in Mizaan that he has munkar narrations. Bukhari has said that there is a question about him. [Imam Bukhari رحمه الله often uses this expression to desribe the weakness of a narrator]. Ibn al Turkmani رحمه الله says, “The mother of Abdul Jabbar is the mother of Yahya. I do no know her name or her details (grade of reliability).” Saeed bin Abdul Jabbar is also weak. Dhahabi quotes Nasai in his Mizaan as saying that Saeed bin Abdul Jabbar is not strong. Hafidh ibn Hajar says in Taqreeb, “Sa'eed bin Abdul Jabbar al Hadhrami al Kufi is weak.” [al T’aleeq al Hasan 1/145]
5. Aqabah bin Sahban رحمه الله reports that Sayyiduna Ali (ra) commenting on the verse [So pray unto thy Lord, and sacrifice] explained, that this means to place the right hand upon the middle of the left upon the chest. [Bayhaqi 2337]
Ibn al Turkmani رحمه الله says that both the sanad and the text of this narration are mudhtarib. [al Jawhar al Naqiyy 2/46]
6. Abu al Jawz رحمه الله reports from Sayyiduna ibn Abbas رضي الله عنهما that he said of the verse [So pray unto thy Lord, and sacrifice]: This means placing the right hand upon the left in prayer, on the chest. [See fn. 305]
Imam Nimawi رحمه الله has declared the isnad of this narration to be weak.
He says,“Rawh bin al Musayyab is matrook [abandoned]. Ibn Hibban says that Rawh Ibn al Musayyab narrates and ascribes fabricated traditions even to reliable authorities. It is not permissible to narrate from him. Ibn Adiyy says that his narrations are not preserved.” [al T’aleeq al Hasan 1/146]
The sanad also contains a third narrator, Amr bin Malik al Nakri. Ibn al Turkmani رحمه الله writes of him in al Jawhar al Naqiyy saying,
“Ibn Adiyy has said that Amr al Nakri is munkar al Hadeeth even when narrating from reliable authorities. He plagiarised narration and Abu Ya’la al Mawsili declared him dhaeef.” [al Jawhar al Naqiyy 2/47]
The correct Tafseer of this verse:
Ibn Jareer at-Tabari رحمه الله, quoting the tafseer of the ulama which he states is the most correct, writes:
“The meaning of this verse is that “Oh Porophet of Allah! Make all your prayers sincere for the sake of your Lord, whithout any share for other false gods and deities, and also make all your sacrifices solely for the sake of your Lord without any share for other idols.” [Ibn Jareer al Tabari in his Tafseer 12/724]
7. Ibn Jarir adh-Dhabbiyy رحمه الله reports from his father who said, “I saw Ali (ra) clasping his left hand with his right on the wrist, above the navel.” [Abu Dawood 757]
Imam Nimawi رحمه الله writes in Aathar al Sunan that the additional wording “above the navel” is not authentic and established. The same hadeeth has been narrated in al Safinah al Jaraidiyyah on the authority of Muslim bin Ibrahim, one of Bukhari’s shaykhs, in al Musannaf of Abu Bakr bin Abi Shaibah, [Ibn Abi Shaibah 3940 & 8722] and in Bukhari [in the chapters relating to actions in salah] in muallaq, abridged form. However, none of these narrations contain the extra wording “above the navel”. The only narrator to include this additional wording in the hadeeth is Abu Badr Shuja bin al Walid رحمه الله narrating from Abu Talut Abdus Salam bin Abi Hazim رحمه الله. Shuja’ has been considered reliable by some, but Abu Hatim رحمه الله says of him as quoted by Hafidh Ibn Hajar رحمه الله in his introduction [to Fath al Bari], and by Dhahabi رحمه الله in his Mizan that “He is weak in hadeeth; a shaykh who is not strong and therefore, his word cannot be acceptable in evidence, although he has saheeh ahadeeth from Muhammad bin Amr bin Alqamah.” Hafidh Ibn Hajar رحمه الله also says in his Taqreeb, “He is pious, sudooq and he has mistakes.” [al T’aleeq al Hasan 1/146]
Furthermore, above the navel does not mean “upon the chest”.
footnote (fn) no. 292 says: Ahmad 21460. Allamah Hashim Sindhi says in Dirham al Surrah p. 113 that both Simak bin Harb and Qabeesah (two of the narrators of this hadeeth) have been disparaged by some of the ulama of jarh and t'adeel.
fn. 293 Ibn Abi Shaibah 3934, Ahmad 21467, Ibn Majah 809 and Tirmidhi 252. Imam Tirmidhi adds that it is a hasan hadeeth.
fn. 294: Ahmad 21464.
fn. 295: Ahmad2146I & 21475. Daruqutni 1087. al T'aleeq al Hasan 1/145
footnote (fn) no. 292: Ahmad 21460. Allamah Hashim Sindhi says in Dirham al Surrah p. 113 that both Simak bin Harb and Qabeesah (two of the narrators of this hadeeth) have been disparaged by some of the ulama of jarh and t'adeel.
fn. 299: al T’aleeq al Hasan 1/145. Allamah Hashim Sindhi says in Dirham al Surrah p27 that the authenticity of two of its narrators has been disputed: Sulaiman bin Musa and Haitham bin Humaid.
fn. 305: Bayhaqi 2339. Allamah Hashim says in Dirham al Surrah p28, “The hadeeth is weak on two accounts: because it is muqati’ and also because three of its narrators, Amr, Yahya and Rawh are weak. So this should be considered. Furthermore, the authors of Muheet al Burhani and Majm’a al Bahrain have narrated a marf’u hadetteh from Ibn Abbas [radiyallahu anhu] with the words “It is part of sunnah to place the right hand upon the left below the navel in salah.”
A more detailed reply can be found in arabic works like:
i) Dirham al-Surra by Imam Muhammad Hashim al Sindi (d. 1174 AH) - which contains a thorough reply to Shaykh Muhammad Hayat al-Sindi and those who imitated him in later times (like Abdur Rahman al Mubarakpuri in his Tuhfatul Ahwadhi)
ii) Athar al-Sunan ma'a Ta'liq al Hasan by Imam al-Nimawi
iii) I'la al-Sunan by Shaykh Zafar Ahmad al-Uthmani (d. 1974)
iv) Badhlul Majhud fi Halli Sunan Abu Dawud by Shaykh Khalil al-Sahranpuri
v) Ma'arif al-Sunan by Shaykh Muhammad Yusuf al Binuri (d. 1977)
The scholars have provided various reasons why the hands are best placed beneath the navel and why this method has been classified as most preferable.
(a) Although most of the ahadith on this issue are weak in one way or another, the narrations presented by the Hanafis have been judged to be more sound than the rest.
(b) Ibn al-Humam رحمه الله states in his book Fath al-Qadir, 'Due to the inconsistency and contradictions found between the various narrations, it is best to resort to analogy and reasoning. Standing before the Lord demands a posture which expresses respect and reverence. Since positioning the hands beneath the navel is probably the most respectful way of standing, it will be considered most superior. On the other hand, the reason for women being instructed to position their hands on their chest, is so that greater concealment [and modesty] can be achieved by this.'
c) Allama Ayni رحمه الله states, 'To position the hands beneath the navel holds great virtue. It is a posture which signifies great respect. It displays greater contrast to the postures of the disbelievers.' He further states, 'Placing the hands on the chest creates a similarity with women, hence that cannot be classified as the sunna for men.' [Umdat al-qari 3:16]
Sayyiduna Wail bin Hujr رضي الله عنه says: 'I saw Rasulullah صلى الله عليه وسلم placing his right hand over his left in prayer, below the navel.
Sayyiduna Ali رضي الله عنه says, 'It is part of he sunnah of prayer to place the palm over the palm below the navel.'
Sayyiduna Abu Hurairah رضي الله عنه says, 'The positioning of the hands upon the hands in prayer is below the navel.' 
Hajjaj bin Hasan رحمه الله said, 'I heard Abu Mijlaz say or I asked him how should I place my hands.' He replied, 'He (the individual performing the prayer) should place the inside of his right palm on his left hand and position both of them below the navel. '
Ibrahim an-Nakha'i رحمه الله reports that Rasulullah صلى الله عليه وسلم would rest one of his hands on the other in salâh, humbling himself before Allâh. Imam Muhammad رحمه الله (the narrator of this hadeeth) says, 'He would place the palm of his right hand on his left wrist below the navel. The wrist would thus be in the middle of the palm.' 
Ibrahim an-Nakha'i رحمه الله also says, 'He (the individual performing the prayer) should place his right hand on his left, below the navel.' 
Imam Tirmidhi رحمه الله says in his Sunan after narrating the above hadeeth of Qabeesah: 'Fastening the hands in prayer is the practice of the learned Sahâbah, Tabi'ûn and Tab' Tabieen رضي الله عنهم. They are of the view that the individual performing the prayer should place his right hand on his left. Some of them then say that he should position them above the navel whilst others contend that they should be placed below the navel. All is permissible in their view.'
 This is only for men. Women should place their hands on their bosoms.
 Ibn Abi Shaibah. Hafidh Qasim bin Qutlubughah says in his takhreej of the ahadeeth of 'al Ikhtiyaar' that this hadeeth has a very good sanad. Imam Hashim Sindhi also says in his Dirham al Surrah p84 that its sanad is strong. Imam Nimawi says that its sanad is saheeh (330). Imam Abu Tayyib Madani also says in his commentary of Tirmidhi 1/277 (published by al Matba' al Nidhami, Kanpur, India, 1299 AH) that this is a hadeeth which is saheeh in both sanad and text and is thus a basis for evidence.
 Ibn Abi Shaibah 3954, Ahmad 877, Abu Dawood 756, Daruqutni 1089 & 1090, and Baihaqi 2341 & 2342. Also narrated by Abu Hafs bin Shaheen in his al Sunnah and by Adani in his Musnad as mentioned by Allamah Hashim Sindhi in Dirham al Surrah, p32 quoting from Kanz al Ummal. Reported also by Razeen as quoted by the author of Jam' al Fawaid.
 Abu Dawood 758 and Ibn Battah as quoted by Allamah Hashim Sindhi in Dirham al Surrah, p36.
 Ibn Abi Shaibah 3942. Ibn at Turkumani says 2/47 that it has been narrated with a very good sanad. Imam Nimawi (331) and Muhaddith Yusuf Binnouri 2/44 both say that its isnad is saheeh. It has also been mentioned by Imam Abu Dawood but without a sanad (757).
 Imam Muhammad in his Kitab al Aathaar 120.
 Ibn Abi Shaibah 3939 and Imam Muhammad رحمه الله in his Kitab al Aathaar 121. Imam Nimawi says that its isnad is hasan (332).
 Tirmidhi 252.
1) The Salah of a Believer in the Qur'an and Sunnah by Shaykhul Hadeeth Riyadh ul Haq
2) Fiqh al-Imam by Mufti Abdur Rahman Ibn Yusuf