Du'aa' can be categorised in a variety of ways, depending on the perspective that one is using. Some of the more useful categorisations are as follows:
1. With Respect to the Actuality of Du'aa'
When one examines the texts of the Qur'an and sunnah, one finds that there are two types of du'aa's that are mentioned.
The first type, which is the one that most people are familiar with, is known as du'aa' al-mas'alah, or the du'aa' of asking. This is when a person asks to be given something that is of benefit to him, or asks that some harm be removed from him. So the worshipper asks Allah سبحانه و تعالى to fulfill a need; for example, he says, "O Allah! Grant me good in this world, and good in the Hereafter!" So this is an example of Du'aa' al-mas'alah.
The second type of Du'aa' is known as Du'aa' al-'ibaadah, or the Du'aa' of worship. This is a very broad concept, for every single act of worship includes in it this type of Du'aa'. Every praise that a person pronounces, every prayer that he performs, is done with an intrinsic plea and cry that emanates from the heart of every believer: "O Allah! I am doing this act of worship because you are All-Mighty and Powerful! You are the only one that deserves all types of praise! O Allah! Accept this act from me!" Therefore, when a person says, 'Alhamdulillaah' or 'SubhaanAllah' this can be taken to be examples of Du'aa' al- 'ibaadah. When a person prays Salaah, or gives Zakaah, or fasts, all of these are examples of Du'aa' al-'ibaadah.
These two types of Du'aa's are inherently related to one another. Every Du'aa' al-mas'alah intrinsically contains a Du'aa' al-'ibaadah, and every Du'aa' al-'ibaadah necessitates a Du'aa' al-mas'alah. To clarify this expression, two examples are given.
When the Muslim prays, "O Allah! Bless me with pious offspring", then this is a clear example of a Du'aa' al-mas'alah, as he is asking for some benefit. However, this simple Du'aa' implies, without him saying anything, that Allah سبحانه و تعالى is the One Who hears his prayer, and responds to it, and He is the One that gives sustenance, and blesses people with offspring. It implies that Allah سبحانه و تعالى is the Ever-Living, the Giver of life, the Ever-Merciful who responds to His servants. This simple Du'aa' necessitates that the person who makes it attributes to Allah سبحانه و تعالى many beautiful and perfect attributes. Thus, this Du'aa' al-mas'alah intrinsically contains Du'aa' al-'ibaadah at the same time.
As a second example, a person says, 'La hawla wa la quwwata ilia billah' or, 'There is no change or power except with the (help and will) of Allah.' At face value, this expression is a Du'aa' al-'ibaadah, as nothing is actually being asked from Allah سبحانه و تعالى. However, this expression necessitates that a person make Du'aa' al-mas'alah to Allah سبحانه و تعالى. When a person affirms that there is no power, nor is it possible to change anything, except with the Will and Permission of Allah سبحانه و تعالى, then this automatically necessitates that he ask Allah سبحانه و تعالى, and only Allah, whenever he wishes to achieve something. So, this Du'aa' al-'ibaadah necessitates Du'aa' al-mas'alah.
So whenever the word Du'aa' occurs in the Qur'an and Sunnah, it has one of three possibilities: it either refers to both types of Du'aa', or it refers to Du'aa' al-mas'alah, or it refers to Du'aa' al-'ibaadah.
An example in which the word Du'aa' refers to both types of Du'aa' is:
"Say (O Muhammad صلى الله عليه وسلم to the disbelievers): "My Lord pays attention to you only because of your invocation to Him. But now you have indeed denied (Him). So the torment will be yours for ever (inseparable permanent punishment)." (Sooratul Furqaan, 25:77)
This verse includes Du'aa' al-mas'alah and Du'aa' al-'ibaadah; in other words, the reason that Allah pays attention to us is because of our worship (Du'aa' al- 'ibaadah) and asking (Du'aa' al-mas'alah) that we do of Him.
An example in which the word Du'aa' primarily refers to Du'aa' al-mas'alah is:
"Or who is there that responds to the call (du'aa') of the one in distress (besides Allaah)?" (Sooratun Naml, 27:62)
An example in which it primarily refers to Du'aa' al-'ibaadah is:
"O mankind! A similitude has been coined, so listen to it (carefully): Verily! Those on whom you call (i.e. worship) besides Allah, cannot create (even) a fly, even though they combine together for the purpose. And if the fly snatched away a thing from them, they would have no power to release it from the fly. So weak are (both) the seeker and the sought. " (Sooratul Hajj, 22:73)
However, even though the direct references in the last two verses are only to one type of Du'aa', indirectly both types are included, as they are inherently related to one another.
2. With Respect to the One Being Asked
Du'aa' is, by its very nature, a call or request to another being. Therefore, it is possible to categorise Du'aa' with respect to the one being asked, for it is possible that the one that is being asked is Allah سبحانه و تعالى, and it is possible that it is a false deity. It is also possible that the person making Du'aa' combines Du'aa' al-mas'alah and Du'aa' al-'ibaadah to the same deity at all times, or he differentiates between them.
So this leads to four categories of people, as follows:
The first category are those people who worship other than Allah سبحانه و تعالى, and call out to these others at all times. These people do not acknowledge Allah سبحانه و تعالى as the Lord or One that deserves worship. Examples of this category are the Hindus, Buddhists, and the followers of other religions who do not believe in Allah سبحانه و تعالى in the first place. So these people direct their Du'aa' al-'ibaadah and Du'aa' al-mas'alah to other than Allah.
The second category are those who believe in Allah سبحانه و تعالى, and worship Him, yet never ask anything of Him. Instead, basing their idea on perverted logic, they use intermediaries in order to approach Allah سبحانه و تعالى, and ask these intermediaries to bless them with what they need. The extreme Sufi groups are notorious for this type of act, for they usually ask dead 'saints' and prophets to bless them with what they need. Therefore, their Du'aa' al-'ibaadah (in the broad sense) is to Allah, but their Du'aa' al-mas'alah is to other than Allah سبحانه و تعالى.
The third category are those people who believe in Allah سبحانه و تعالى, and worship Him, but only turn to Him at times of severity. When they are in extremely desperate situations, they combine their Du'aa' al-'ibaadah and Du'aa' al-mas'alah to Allah, but at times of ease, they call out to other than Allah. And this was the religion of the Jaahiliyyah Arabs at the time of the Prophet صلى الله عليه وسلم.
The last category are the true Muslims, those that always combine Du'aa' al-'ibaadah and Du'aa' al-mas'alah, and direct it to Allah سبحانه و تعالى, and only to Allah سبحانه و تعالى. So they direct their worship, prayer, and charity, to Allah سبحانه و تعالى, and they turn to Him only for all of their needs.
3. With Respect to the One Making Du'aa'
When one looks at the different categories of people that make Du'aa', it is possible to classify them into four categories.
This is because Du'aa', as has been mentioned, is of two types, Du'aa' al-'ibaadah and Du'aa' al-mas'alah. Therefore, it is possible to have four logical combinations of these categories with regards to the one making Du'aa', for he can either combine both types of Du'aa', or practice only one type, or leave both types. (Note that this categorisation contains some overlap with the preceding one, but at the same time is unique, as it deals with the one asking, and not the one that is asked).
The first category of people are those who combine both types of Du'aa', and this is the way of the true Muslim. So he worships Allah سبحانه و تعالى, realising that this worship is the purpose of his creation and being, and he seeks Allah's help in this worship, realising that without this help he will not be able to achieve this goal. Therefore, he has combined Du'aa' al-'ibaadah with Du'aa' al-mas'alah.
Allah سبحانه و تعالى combined these two types of Du'aa's in numerous verses in the Qur'an, the simplest of them being the oft-recited verse:
"You (Alone) we worship, and you (Alone) we ask for help (for each and everything)." (Sooratul Faatihah, 1:5)
So this verse clearly shows the important relationship between Du'aa' al-'ibaadah , and Du'aa' al-mas'alah, and the wise person is he who understands and acts upon both of these types of Du'aa' in his life.
The second category of people are those that have left both types of Du'aa', so they neither worship Allah سبحانه و تعالى, nor seek His help or aid in any matter. So in this category fall the people that worship false deities, believing these deities to be worthy of their Du'aa' al-'ibaadah and Du'aa' al-mas'alah. They never turn to Allah سبحانه و تعالى, and thus have lost this world and the Hereafter.
Also, those that have rejected religion entirely, such as the communists, atheists and agnostics, fall into this category as well. To such people, the only way to achieve any goal is through physical means, for in their rejection of a god they have implicitly worshipped creation. And these are the worst of mankind.
The third category are those people that practice Du'aa' al-'ibaadah, but ignore Du'aa' al-mas'alah. Such thinking can only come from an ignorant person, or one who is deviated in his beliefs.
As for the ignorant Muslim — and unfortunately how common they are in our times — then he forgets that the real way and sure path to achieve his goal is by making Du'aa' to Allah سبحانه و تعالى. He becomes so caught up in this world that, although he might pray and fast and give Zakaah, he forgets the spiritual aspect of Islam, and the beauty of the Names and Attributes of Allah سبحانه و تعالى. To such a person, Islam becomes a series of mundane acts, devoid of any meaning, performed at regular intervals. Such a person needs to re-evaluate his concept of Islam, and even of life, in order that he can correct his misunderstanding. He must ponder over the meanings of the Names and Attributes of Allah سبحانه و تعالى, and realise the ultimate Power and Knowledge of the Creator, and only then will he be able to see the error of his ways. He must realise that every act he does, whether it is related to this world or the Hereafter, must be done with the help and aid of Allah سبحانه و تعالى, for if Allah سبحانه و تعالى does not help him in achieving what he desires, he will never be able to achieve it.
As for the person who actually believes that it is incorrect to use Du'aa' al-mas'alah, and instead restricts himself to Du'aa' al-'ibaadah, then such a person without a doubt has committed a grave mistake. These people are only found in deviated sects — sects that have perverted the meanings of the Qur'an and Sunnah in order to justify their positions. Examples of this are the extreme Sufis, for many of them believe that it is actually a sin to ask Allah سبحانه و تعالى for anything! Basing this belief on a few fabricated ahaadeeth, they claim that a person must always be content with what Allah سبحانه و تعالى decrees for him, and therefore should not pray for a change in his situation! The falseness of this logic is in their understanding of 'contentment,' for to be content with Allah سبحانه و تعالى means that one should not curse the Divine Decree, or be angry at Allah سبحانه و تعالى for what has occurred. It does not mean that one must be happy and satisfied at every incident that occurs to one, particularly if it is related to a sin or an evil pertaining to one's religion. In addition, we find that all of Allah's prophets, without exception, made Du'aa' to Allah سبحانه و تعالى for all matters. Therefore, this understanding of the extreme Sufis is not in accordance with the understanding of the prophets عليهم الصلاة والسلام.
The fourth, and final, category are those people that ignore Du'aa' al-'ibaadah, and only practice Du'aa' al-mas'alah. Such people believe in Allah سبحانه و تعالى, but follow their own selfish desires, and strive in order to satisfy their every whim. So they leave worship of Allah سبحانه و تعالى, but they realise that Allah is the Controller of all affairs, and, therefore, ask Him for their selfish needs.
The primary example of this is Iblees, Satan himself, may Allah's eternal curse be upon him. For when he was expelled from Paradise due to his arrogance, he actually made a Du'aa' to Allah سبحانه و تعالى, Du'aa' al-mas'alah — to allow him to live until the Day of Judgement. And Allah سبحانه و تعالى responded to his Du'aa' and granted him his wish, even though Iblees knew full well that this time that he was granted would only be used to mislead others, out of his spite and jealousy. So Iblees left Du'aa' al-'ibaadah out of arrogance, but was forced to use Du'aa' al-mas'alah out of greed.
Likewise, all those who have preferred the life of this world over the Hereafter have fallen into the same mistake as Iblees.
Allah سبحانه و تعالى states in the Qur'an:
"And when you have completed your rites, remember Allah like your [previous] remembrance of your fathers or with [much] greater remembrance. And there are those amongst mankind who say, 'O Allah! Give us in this life,' and they will have no share of the Hereafter. And there are those who say, 'O Allah! Give us good in this life, and good in the Hereafter, and save us from the Fire of Hell.' These shall have a share of what they earned, and Allah is swift in Reckoning." (Sooratul Baqarah, 2:200-202)
So these are the four categories of people when it comes to practicing both categories of Du'aa'.
4. With Respect to What is Asked
The actual Du'aa' itself can be categorised in many different ways, depending on which perspective one looks from.
So, it is possible to divide what is asked for into two categories: matters pertaining to religion, and matters pertaining to the world. Examples of the first type are to ask for increased faith, or an increase in good deeds, or forgiveness for one's sins. Examples of the second category are to ask for an increase in money, or to be cured from a disease, or to be granted more children.
The true Muslim asks Allah سبحانه و تعالى from both of these categories, realising that the good pertaining to this world is in reality a means of attaining the good in the Hereafter. So, an increase in wealth, children, and health is in fact a means of coming closer to Allah سبحانه و تعالى by obeying His commandments and sacrificing in His way. On the other hand, ignorant and deviated Muslims will only ask Allah سبحانه و تعالى for one of these two categories, ignoring the other.
Another way to categorise what is asked for is by examining the benefit or harm it causes. So, it is possible to state that the entire Du'aa' of all of creation centres around four pillars:
Firstly: good that exists. For example, one might be in a state of good health, or have great wealth. So Du'aa' is made that this state lasts, and is not taken away.
Secondly: good that is desired. For example, a person does not have good health, but wishes for it This is asked for by means of Du'aa'.
Thirdly: evil that exists. For example, a person might be sick, or suffer from poverty. So Du'aa' is made that this situation be changed.
Fourthly: evil that does not exist. For example, a person might fear a certain disease, or another trial. So Du'aa' is made that this evil never occurs, and is averted.
All of these four types of Du'aa' are combined in the comprehensive Du'aa' that is found in the last verses of Soorah Aaali 'Imraan:
"'Our Lord! Verily, whom You admit to the Fire, indeed, You have disgraced him, and for the wrongdoers there are no helpers. Our Lord! Verily, we have heard the call of one (Muhammad صلى الله عليه وسلم) calling to Faith: "Believe in your Lord," and we have believed. Our Lord! Forgive us our sins and remit from us our evil deeds, and make us die in the state of righteousness along with Al-Abraar (those who are obedient to Allah and follow strictly His Orders). Our Lord! Grant us what You promised unto us through Your Messengers and disgrace us not on the Day of Resurrection, for You never break (Your) Promise.'" (Soorah Aaali 'Imraan, 3:193-194)
So the phrase, 'Forgive us our sins, and remit us from our evil deeds,' is a Du'aa' that an existing evil be removed. And the phrase, 'and cause us to die in a state of righteousness,' is a Du'aa' asking that an existing good, that of the presence of eemaan (faith), continue and not be taken away until death. And the phrase, 'Grant us what you promised us through Your messengers', is a Du'aa' for a good that does not yet exist to be given. Lastly, the phrase, 'do not disgrace us on the Day of Judgement', is a Du'aa' to avert an evil that does not exist.
[Dua: The Weapon of the Believer]