As we know, the tradition or ahadith of the Holy Prophet (S) recorded in the books of Muslim traditionists begin with chains of transmitters on whose authority the traditionist reports the Prophet's acts or statements. Experts of hadith amongst Muslims have developed certain criteria for assessing the reliability of different chains of transmission and ascertaining the authenticity of the contents of traditions. They have developed a terminology with terms denoting various classifications of hadith depending on the character, strength or weakness of narrators and other factors, such as mutawatir, ahad, sahih, hasan, qawi, da`if, etc.
By tawatur is meant the multiplicity of the sources of a certain report that leads to certitude in the listener that the report is indeed true. One's knowledge of the existence of distant countries and towns and such historical figures as Cyrus or Napolean may be said to be based on the tawatur of reports that one hears about them. So also is one's knowledge of the contemporary events not witnessed by him.
A mutawatir hadith is one which has been reported by so many different chains of transmission and such a number of narrators in every generation as normally could not agree to fabricate a tradition without the fact of its fabrication becoming known. Although some jurisprudents have specified a particular minimum for the number of narrators, such as five, seven, ten or even hundred, it is generally held that no particular number can be specified and the number capable of producing certitude depends on the experience of the listener.