`Abd al-Kahir b. Tahir, Abu Mansur al-Shafi`I al-Baghdadi (d. 429/1037)
Al-Baghdadi grew up in Nishapur, where his father had brought him for his education. He was well versed in law, mathematics and literature. Most of the scholars of Khurasan were his students. He taught arithmetic, theology, law, rules of inheritance, principles and other subjects.
Kitab al-Milal wa ‘l-Nihal (a book on theology, which is lost)
Usul al-Din (a systematic tratise, beginning with the nature of knowledge, creation, how the Creator is known, His attributes)
al-Rark bayn al-Firak ( a polemic, judging all sects from the standpoint of orthodoxy, ending with an exposition of orthoox belief).
The Errors of Abu ‘l-Hudhayl (which is lost)
Errors of ibn Karram (which is lost)