A
hadith is a saying of Muhammad or a report about something he did. Over time, during the first few centuries of Islam, it became obvious that many so-called hadith were in fact spurious sayings that had been fabricated for various motives, at best to encourage believers to act righteously and at worse to corrupt believers' understanding of Islam and to lead them astray. Since Islamic legal scholars were utilizing hadith as an adjunct to the Qur'an in their development of the Islamic legal system, it became critically important to have reliable collections of hadith. While the early collections of hadith often contained hadith that were of questionable origin, gradually collections of authenticated hadith called
sahih (lit. true, correct) were compiled. Such collections were made possible by the development of the science of hadith criticism, a science at the basis of which was a critical analysis of the chain of (oral) transmission
(isnad) of the hadith going all the way back to Muhammad. The two most highly respected collections of hadith are the authenticated collections the Sahih Bukhari and Sahih Muslim. (
Sahih literally means "correct, true, valid, or sound.")

Hadith Collections