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 clarify that term and not necessarily establish it. He also distinguished his book by responding to the positions of other scholars in a detailed manner. Ibn al-Ṣalāḥ mentioned in his introduction to the "Introduction" 65 chapters, each specific to a particular type or term of hadith terminology before saying that an even larger number was conceivable. He began by discussing "ṣaḥīḥ" (authentic) as the first category, and then "ḥasan" (good) as the second, "ḍa`īf" (weak) the third, "musnad" (supported) the fourth and so on. Ibn Jamāʻah, in his abridgement, divided these terms into four different categories according to subject (and