Hadith are "expressed in Muhammad's words", whereas the latter are the "direct words of God". A "hadith qudsi" need not be a "sahih" (sound hadith), but may be "da‘if" or even "mawdu‘". An example of a "hadith qudsi" is the hadith of Abu Hurairah who said that Muhammad said: When God decreed the Creation He pledged Himself by writing in His book which is laid down with Him: My mercy prevails over My wrath. In the Shia school of thought, there are two fundamental viewpoints of Hadith: The Akhbari view and the Usuli view. The Usuli scholars stress the importance of
Introduction to the Science of Hadith al-Ṣalāḥ, in his "Introduction", codified the terminology established by those scholars before him based upon his reading of their works. He did so by citing some of those scholarly statements in the earlier works and deducing from them common terms and definitions in the manner of a scholar authoring a book of "fiqh" (jurisprudence). In this manner, his book was based upon those principles established by the earlier hadith specialists combined with some elements of "fiqh". An example of this would be the inclusion of the division of hadith into "mutawātir" and "āḥād". He therefore only mentioned the statements of