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 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