Hadit, (Arabian, narrative) are accounts of Muslim tradition, containing "words, deeds, or silent approval" of Muhammad during his teaching period, but especially after the beginning of the Qur'an revelations. The words and deeds, or sayings, are separately referred to as the hadits, but collectively as the hadith. Muhammad's Companions and Successors had their own hadith. The original collections have vanished being superseded by more comprehensive ones composed in the ninth century. They were of two types:the musnad, in which the hadiths are classified on the basis of the Companions who transmitted them, and the musannaf, in which they are arranged in accordance to their subject matter.
The hadith speaks of the customary practice, sunna, of Muhammad, or his Companions, and given extra authority by a Quranic reference. For example, the Qur'an speaks of the Book and Wisdom which Muhammad taught to the believers, and the wisdom, hikma, was referring to the hadith, which, in time, became the second source of legislation after the Qur'an.
A hadith, or single item of tradition, consisted of to parts: the matn ("text") and the isnad or sanad (chain of authorities). The latter was a listing of men, who heard it from whom. Eventually there evolved an elaborate science of hadith criticism around any given hadith, and each one was classified as "sound," "good," or "weak," while more detailed classifications dealt with the authorities cited.
This highly developed criticism not only developed from a purely devotional desire to follow the exact way of Islam but because of other reasons as well, which involved political, personal, and religious motives. The various reasons included support for the Umayyads or Abbasids (political groups), malice from those desiring to discredit Islam, to gain more free will as urged by the Shiites, and those urging works of piety. There is evidence some fabricated hadiths for economic gain-story tellers lived by spinning good yarns, and merchants made money by indicating the Prophet loved pumpkins or whatever.
However, the fact is that the fabric of Islamic communities and culture is indebted more to hadiths than to the Qur'an. Almost every aspect of Muslim life is centered on some saying or action of the Prophet, which gives the aspect its approval or disapproval. Most of this information is simply learned by being born and bred in Muslim society. But, devout Muslims having studied the hadiths are more able to emulate the Prophet in their lives.