Although the task of preserving of Ahadith through all the four ways mentioned earlier including compilations in written form, has been performed with due diligence throughout the first four centuries of Islamic history, yet it does not mean that all the traditions narrated or compiled in this period have been held as true and reliable.
In fact, in the same period in which the work of the compilation of Ahadith was going on, a very systematic science of criticism was developed by the scholars of hadith in which numerous tests were suggested to verify the correctness of a narration. All these tests were applied to each and every tradition or report before holding it reliable. The different branches of knowledge, which have been introduced by the scholars of the science of hadith, have no parallel in the art of historical criticism throughout world history. It is not possible for us to herein present even a brief introduction of these different branches and the valuable works produced in this respect. It may be said without any fear of exaggeration that thousands of books have been written on these different branches of knowledge regarding the science of hadith.
It will be pertinent, however, to give a brief example of the nature of the Criticism of Ahadith carried on by scholars and the different tests applied by them to ascertain the veracity of a hadith.
The traditions viewed from different angles have been classified into hundreds of kinds. Relative to their standards of authenticity, the traditions are ultimately classified into four major categories:
(a) Sahih (correct)
(b) Hasan (good enough)
(c) Da’if (weak)
(d) Maudu’ (coined)
Only the first two kinds are held to be reliable. Precepts of the Shari’ah can be based on and inferred from only these two kinds. Hence, only the Ahadith of these two categories are held to be the source of Islamic law. The other two kinds have little or no value especially in the legal or doctrinal matters.
Before declaring a hadith as Sahih or Hasan, the following tests are applied: –
(a) Scrutiny of its narrators.
(b) Scrutiny of the constancy of the chain of narrators.
(c) Comparison of its chain and text with other available ways of narration in the same matter.
(d) Examination of the chain and the text of the hadith in the light of other material available on the subject, and to ensure that there is no defect in the chain or in the text.
We will try to give a brief explanation of these four tests as they are applied by the scholars of hadith to scrutinize the veracity of a tradition.