Hadith same text are each counted as individual ahadith. If, say, ten companions record a text reporting a single incident in the life of Muhammad, hadith scholars can count this as ten hadiths. So Musnad Ahmad, for example, has over 30,000 hadiths—but this count includes texts that are repeated in order to record slight variations within the text or within the chains of narrations. Identifying the narrators of the various texts, comparing their narrations of the same texts to identify both the soundest reporting of a text and the reporters who are most sound in their reporting occupied experts of hadith
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