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 "with something, such as numerous chains of narration, strengthening it." Ibn Hajar's definitions indicate that there are five conditions to be met for a particular "hadith" to be considered "ṣaḥīḥ": A number of books were authored in which the author stipulated the inclusion of "ṣaḥīḥ hadith" alone. According to Ahl al-Sunna, this was only achieved by the first two books in the following list: "Ḥasan" ( meaning "good") is used to describe "hadith" whose authenticity is not as well-established as that of "ṣaḥīḥ hadith", but sufficient for use as supporting evidence. Ibn Hajar defines a "hadith" that is "ḥasan lithatihi"""ḥasan"