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,
Hadith terminology terminology, it refers to a "hadith" not fulfilling all of the conditions necessary to be deemed "mutawatir". "Hadith ahad" consists of three sub-classifications also relating to the number of narrators in the chain or chains of narration: An "ʻaziz" () "hadith" is any "hadith" conveyed by two narrators at every point in its "isnād" (chain of narrators). A "gharib" () "hadith" is one conveyed by only one narrator. Al-Tirmidhi's understanding of a "gharib hadith", concurs to a certain extent with that of the other traditionists. According to him a "hadith" may be classified as "gharib" for one of the following