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-Kattānī. `Āʼishah bint `Abd al-Raḥmān said in the foreword of her edition of the "Introduction": His book about the sciences of hadith is the best known of his works without comparison, to the extent that it is sufficient to say, "the Book of Ibn al-Ṣalāḥ", the intent being understood due to its popularity and stature. With the previous scholars, its subject matter overcame it, thus being referred to as, "the Book of Ibn al-Ṣalāḥ about `Ulūm al-Ḥadīth" or as he referred to it in its opening pages, "the Book of Familiarity with the Types of `Ulūm al-Ḥadīth". It has become