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,
Criticism of Hadith highly of Mutawatir: However, orthodox hadith scholars find non-mutawatir hadith adequate. "According to the majority of the ulama of the four Sunni schools, acting upon ahad is obligatory even if ahad fails to engender positive knowledge. Thus, in practical legal matters," but not in "matters of belief", "a preferable "zann" [meaning, speculative] "is sufficient as a basis of obligation." Ibn al-Salah ( (d. 643/1245), "one of the most distinguished traditionists of the muta'akhkhirun", argues (according to Farooq), that because mutawatir type hadith is rare, "for much of Islamic praxis, certainty of knowledge is neither feasible nor required. Rather, probable or