During the first few decades after the Prophet Muhammad's death, those who directly knew him (known as the Companions) shared and collected quotations and stories related to the Prophet's life. Within the first two centuries after the Prophet's death, scholars conducted a thorough review of the stories, tracing the origins of each quotation along with the chain of narrators through whom the quotation was passed. Those which were not verifiable were deemed "weak" or even "fabricated," while others were deemed "authentic" (sahih) and collected into volumes. The most authentic collections of hadith (according to Sunni Muslims) include Sahih Bukhari, Sahih Muslim, and Sunan Abu Dawud.
Each hadith, therefore, consists of two parts: the text of the story, along with the chain of narrators which support the authenticity of the report.
The hadith are considered by most Muslims to be an important source of Islamic guidance, and are often referred to in matters of Islamic law or history.