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 According to Racha El Omari, early Mutazilites believed that hadith were susceptible to "abuse as a polemical ideological tool"; that the "matn" (content) of the hadith -- not just the "isnad" -- ought to be scrutinized for doctrine and clarity; that hadith "supported by some form of "tawātur"", i.e. by a large number of "isnād" strands, each beginning with a different Companion, were valid. In writing about "mutawatir" (transmitted via numerous chains of narrators) and "ahad" (any ahadith that is not "mutawatir") and its importance from the legal theoretician's point of view, Wael Hallaq notes the medieval scholar Al-Nawawi argued