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 in and of itself"with the same definition a "ṣaḥīḥ hadith" except that the competence of one of its narrators is less than complete; while a "hadith" that is "ḥasan ligharihi" ("ḥasan due to external factors") is determined to be "ḥasan" due to corroborating factors such as numerous chains of narration. He states that it is then comparable to a "ṣaḥīḥ hadith" in its religious authority. A "ḥasan hadith" may rise to the level of being "ṣaḥīḥ" if it is supported by numerous "isnād" (chains of narration); in this case that "hadith" would be "ḥasan lithatihi" (""ḥasan" in and of itself")