Abu Mansur 'Abd al-Qahir ibn Tahir al-Baghdadi (Arabic: أبو منصور عبدالقاهر ابن طاهر بن محمد بن عبدالله التميمي الشافعي البغدادي) was a Shafi'i scholar, Imam in fundamentals of Islam (Usul), heresiologist and mathematician.
'Abd al-Qahir al-Baghdadi was born and raised in Baghdad. He received his education in Nishabur and subsequently taught 17 subjects, including law, usul, arithmetic, law of inheritance and theology. Most of the scholars of Khurasan were his pupils.
'Abd al-Qahir al-Baghdadi wrote several books including Usul al-Din, a systematic treatise, beginning with the nature of knowledge, creation, how the Creator is knos attributes, etc.... and al-Farq bayn al-Firaq which takes each sect separately, judges all from the standpoint of orthodoxy and condemns all which deviate from the straight path. Both books were major works on the beliefs of Ahl al-Sunna.
He also wrote the treatise al-Takmila fi'l-Hisab which contains results in number theory, and comments on works by al-Khwarizmi which are now lost.
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