Hadith of the Quran and Sunnah al-Thaqalayn" multiple times in multiple settings in multiple wordings. They argue that Muhammad said "Hadith al-Thaqalayn" at Mount Arafat during his Farewell Sermon, at Ghadir Khumm, in the mosque of Medinah, during his last illness, and at many other places and times. The Shi'as believe that Muhammad said this hadith so many times because he wanted to stress how important it was that the Muslims only take his own descendants as leaders. The Shi'as believe that this hadith is mutawattir, meaning that it has been related so many times by so many people that there is no doubt about its
Introduction to the Science of Hadith category, which comprises 21 types, relates to the names of the narrators. This includes the definition of a "ṣaḥābī" (companion), a "tābi`ī" (follower), the time periods of narrators, names and paidonymics among others. Later scholars included additional types of hadith in their own works, with some almost reaching 100. The "Introduction" became the basis for subsequent books in hadith terminology. A number of subsequent scholars followed Ibn al-Ṣalāḥ in the ordering of his book, including al-Nawawī, Ibn Kathīr, al-ʻIraqi, al-Bulqīnī, Ibn al-Jamā`ah, al-Tabrīzī, al-Ṭībī and al-Zirkashī. In many instances this influence was direct, with numerous scholars authoring books indicating its