The Imams of hadith have divided the hadiths into three different categories: Mutawatir [continuously recurrent], Mashhur [well-known], and Khabar-al-Wahid [a single person’s report] AKA Hadith Ahad [solitary hadith].

A Mutawatir hadith is one for which the narrators are so numerous in any given era that it is virtually impossible for such a large number of people to agree on a fabrication or an error. Examples of this include the existence of London and New York, or the number of Rak'ats in Salah, or the number of Fasts to be observed in Ramadan.

The second type of hadith is called Mashhur. This category is similar to Mutawatir in some respects. The only difference of opinion lies in the number of narrators required for a Mutawatir narration and whether a Mashhur narration should be classified in the category of Mutawatir or Khabar-al-Wahid, or whether it
should be a separate category.

Therefore, we only wish to discuss the third type of hadith, i.e. Khabar-al-Wahid. This category refers to those hadiths which do not reach the standards of Mutawatir. Most narrations fall under this category.
First of all, this type of narration is divided into two types: Accepted [Maqbul] and Rejected [Mardud]. The great hadith master Ibn Hajar al-Asqalani says, “Besides Mutawatir Hadiths—which are undoubtedly acceptable—all other types of hadiths can be divided into two categories: Maqbul and Mardud. Maqbul is that type of hadith upon which practicing is obligatory. Mardud is that hadith the reliability of which supersedes its unreliability. Therefore, a hadith which is comprised of contradictory angles, in other words some angles pointing to its authenticity and reliability and others indicating its unreliability, will fall under the category of Rejected [Mardud]. However, if the angles warranting its acceptability are predominant then the hadith will fall under the category of Reliable[Maqbul]."
Thereafter, Ibn Hajar says that a Rejected [Mardud] Hadith is not necessary to practice upon.
However, Acceptable [Maqbul] Hadiths are of two types: those that are necessary to practice upon and those that are not necessary to practice upon. In other words, a Hadith can technically be an accepted Hadith [Maqbul], but due to some reason or another it is not necessary to practice upon it.
Ibn Hajar further states, “At times an Accepted Hadith is not necessary to practice upon in spite of it being an Accepted Hadith, because of its contradiction with another Hadith. In such a case, both Hadiths will be compared to see if some harmony can be brought about between both. For instance, the scholars have brought about some harmony in the following two contradictory hadiths. The first hadith states, "There is no such thing as contagious diseases in Islam"
while another hadith states, "Flee from a leper as you would flee from a lion." There is an apparent contradiction between these two Hadiths, though both of them are authentic and reliable. The scholars have brought about some harmony between these two hadiths in various forms.

The aim (here) is not to elaborate on their opinions. Only to say that, where there is an apparent contradiction, the first and foremost step will be to bring about some harmony between them. Conversely, if no harmony can be brought about between them, then The Scholars of Hadith will assess whether one has precedence over the other, either in terms of its date or its occurrence. If this can be established, then the latter of the two will be accepted and practiced upon. If this is not possible, The Scholars of Hadith would search for an external reason to grant preference to one over the other. However, if this proves futile, both narrations—in spite of being authentic—would be included in the category of Rejected [Mardud] Hadiths, because of their apparent contradiction.


Taken From the Book "The Differences of the Imams"