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,
Introduction to the Science of Hadith well known as of late as: "Muqaddimah Ibn al-Ṣalāḥ fi `Ulūm al-Ḥadīth", "Ibn al-Ṣalāḥ's Introduction to the Sciences of Hadith". Nūr al-Dīn `Itr, in the introduction to his edition of the "Introduction", concluded that its actual name is either "ʻUlūm al-Ḥadīth" ("The Sciences of Hadith") or "Ma`rifah Anwā`i `Ilm al-Ḥadīth" ("Familiarity with the Types of the Science of Hadith"). This is based upon the author's own usage in his own introduction in addition to the usage of other scholars in the centuries after the authoring of the book. Similar to Bint `Abd al-Raḥmān, he acknowledged that the book is most