In order to know how Muslims deal with Hadith of Mohameed (puh) ,you must know what Muslims mean by The science of Hadith in Islam ,It is very important and clear science ,in it Muslims follow certain Methodology to recognize the degree of accuracy of the Hadith , if you want to understand it you must know about The Classification of Hadith - According to the reliability and memory of the reporters Under this classification falls the final verdict on a hadith, being one of the following: sahih, hasan, da'if or maudu'.
Among the early traditionists, mostly of the first two centuries, ahadith were classified into two categories only: sahih and da'if; al-Tirmidhi was to be the first to distinguish hasan from da'if. This is why traditionists and jurists such as Ahmad, who seemed to argue on the basis of da'if ahadith sometimes, were in fact basing their argument on the ahadith which were later to be known as hasan.
We now examine in more detail these four important classes of ahadith.
Al-Shafi'i states the following requirement in order for a hadith which is not "mutawatir”
( the Hadith which was transferred from one person to another until reach the original resource which was the saying of prophet Mohameed (PUH) )to be acceptable:
"Each reporter should be trustworthy in his religion; he should be known to be truthful in his narrating, to understand what he narrates, to know how a different expression can alter the meaning, and report the wording of the hadith verbatim, not only its meaning. This is because if he does not know how a different expression can change the whole meaning, he will not know if he has changed what is lawful into what is prohibited. Hence, if he reports the hadith according to its wording, no change of meaning is found at all. Moreover, he should be a good memoriser if he happens to report from his memory, or a good preserver of his book if he happens to report from it. He should agree with the narrations of the huffaz, if he reports something which they also do. He should not be narrate from someone he met something he did not hear, nor should he report from the Prophet contrary to what reliable sources have reported from him. In addition, the one who is above him (in the isnad) should be of the same quality until the hadith goes back uninterrupted to the Prophet or any authority below him."
Ibn al-Salah, however, defines a sahih hadith more precisely by saying:
"A sahih hadith is the one which has a continuous isnad, made up of reporters of trustworthy preservers from similar authorities, and which is found to be clear from any defects."
By the above definition, no room is left for any weak hadith.
Of all the collectors of hadith, al-Bukhari and Muslim were greatly admired because of their tireless attempt to collect sahih hadith only. It is generally understood that the more trustworthy and of good memory the reporters, the more authentic the hadith. The isnad: al-Shafi'i --- Malik --- Nafi' --- 'Abdullah b. 'Umar --- The Prophet, is called a "golden isnad" because of its renowned reporters.
Al-Tirmidhi means by hadith hasan, a hadith which is not shadhdh, which does not contain a disparaged reporter in its isnad, and which is reported through more than one route of narration.
Al-Khattabi (d. 388) states a very concise definition,
"It is the one where its source is known and its reporters are prominent."
By this he means that the hadith should not be of an ambiguous nature like the mursal or munqati' hadith, or one containing a mudallis.
Ibn al-Salah classifies hasan into two categories:
(i) one with an isnad containing a reporter who is mastur (i.e., no prominent person reported from him) but is not totally careless in his reporting, provided that a similar text is reported through another isnad as well;
(ii) one with an isnad containing a reporter who is known to be truthful and reliable, but is a degree less in his preservation of hadith in comparison to the reporters of sahih ahadith.
In both categories, Ibn al-Salah requires that the hadith be free of any shudhudh.
Al-Dhahabi, after giving the various definitions, says, "A hasan hadith is one which excels the da'if but nevertheless does not reach the standard of a sahih hadith."
Reporters such as al-Harith b. 'Abdullah, 'Asim b. Damura, Hajjaj b. Artat, Khusaif b. 'Abd al-Rahman and Darraj Abu al-Samh attract different verdicts: some traditionists declare their ahadith hasan, others declare them da'if.
According to the definition of al-Tirmidhi and Ibn al-Salah, a number of weak ahadith on a particular issue can be raised to the degree of hasan if the weakness found in their reporters is of a mild nature. However, in case the weakness is severe, (i.e., the reporter is a liar or the hadith is itself shadhdh), such weak ahadith will not support each other and will remain weak. For example, the famous hadith,
"He who preserves forty hadiths for my Ummah will be raised by Allah on the Day of Resurrection among the Fuqaha' ", has been declared to be da'if by most of the traditionists, although it is reported through various routes.
A hadith which fails to reach the status of hasan is da'if. Usually, the weakness is one of discontinuity in the isnad, in which case the hadith could be mursal, mu'allaq, mudallas, munqati' or mu'dal, according to the precise nature of the discontinuity, or one of a reporter having a disparaged character, such as due to his telling lies, excessive mistakes, opposition to the narration of more reliable sources, involvement in innovation, and ambiguity surrounding his own person.
The smaller the number and importance of defects, the less severe the weakness. The more the defects in number and severity, the closer the hadith will be to being fabricated.
Some ahadith, according to the variation in the nature of the weakness associated with its reporters, rank at the bottom of the hasan grade or the top of the da'if grade. Reporters such as 'Abdullah b. Lahi'a, 'Abd al-Rahman b. Zaid b. Aslam, Abu Bakr b. Abi Maryam al-Himsi, Faraj b. Fadala, Rishdin b. Sa'd and the like, attract such types of varying ranks as they are neither extremely good preservers nor totally abandoned.
Al-Dhahabi defines it as a hadith, the text of which goes against the established norms or its reporters include a liar, e.g. the forty ahadith known as Wad'aniyya or the copy of 'Ali al-Rida which was fabricated against him.
A number of traditionists have collected fabricated ahadith separately in order to distinguish them from other ahadith; among them are Ibn al-Jauzi in al-Maudu'at, al-Janzaqani in Kitab al-Abatil, and al-Suyuti in al-La'ali al-Masnu'a fi al-Ahadith al-Maudu'a.
Some of these ahadith were known to be spurious by the confession of their inventors. For example, Muhammad b. Sa'id al-Maslub used to say, "It is not wrong to fabricate an isnad for a sound statement." Another notorious inventor, 'Abd al-Karim Abu al-Auja, who was killed and crucified by Muhammad b. Sulaiman b. 'Ali, governor of Basra, admitted that he had fabricated four thousand ahadith declaring lawful the prohibited and vice-versa.
Maudu' ahadith are also recognised by external evidence related to a discrepancy found in the dates or times of a particular incident.
Ibn Maja, has given more examples of fabricated ahadith under the following eight categories of causes of fabrication:
factions based on issues of creed;
fabrications by zanadiqa;
fabrications by story-tellers;
fabrications by ignorant ascetics;
prejudice in favour of town, race or a particular imam;
inventions for personal motives;
proverbs turned into ahadith.