Hadith root of why there is no single "fiqh" system, but rather a collection of parallel systems within Islam. Much of early Islamic history available today is also based on the hadith, although it has been challenged for its lack of basis in primary source material and the internal contradictions of the secondary material available. Hadith may be "hadith qudsi" (sacred hadith) — which some Muslims regard as the words of God (Arabic: Allah) — or "hadith sharif" (noble hadith), which are Muhammad's own utterances. According to as-Sayyid ash-Sharif al-Jurjani, the hadith qudsi differ from the Quran in that the former
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