Hadith remembers God unceasingly. (Al-Ahzab 33: 21) The hadith literature is based on spoken reports in circulation after the death of Muhammad. Unlike the Qur'an, ahadith were not promptly written down during Muhammad's life or immediately after his death. Hadith were evaluated and gathered into large collections during the 8th and 9th centuries, generations after the death of Muhammad, after the end of the era of the "rightful" Rashidun Caliphate, over from where Muhammad lived. "Many thousands of times" more numerous than Quranic verse, ahadith have been described as resembling layers surrounding the “core” of the Islamic belief (the Quran). Well-known,
Introduction to the Science of Hadith chapters, each covering a hadith related issue. The first 33 chapters describe the various technical terms of hadith terminology which describe the conditions of a hadith's authenticity, or acceptability as a basis for Islamic jurisprudence. The following chapters relate to the "isnād", or chain of narration. Next are a series of chapters pertaining to the etiquette to be observed by hadith scholars and manners of transcription. The last chapters describe various issues relating to the narrators of hadith including naming conventions. Ibn al-Ṣalāḥ began the "Introduction" as a series of lectures he dictated to his students in Damascus ending in