Also known as al-Qummi and al-Saduq. Twelver Shii scholar and the leader of the traditionists in Qom, Iran. Recorded and preserved traditions transmitted from Muhammad and the imams in the cities of Qom, Rayy, Mashhad, Nishapur, Baghdad, Kufa, Mecca, Hamdan, Balkh, and Samarqand. Made a thorough scrutiny of hadith transmitters and integrated the principles of Islamic law exclusively contained in Imami hadith. Disapproved of the rationalist appraisal of religious questions, even in defense of Shii doctrine. His approach was denounced by his student al-Shaykh al-Mufid (d. 1022), a rationalist theologian. Composed more than two hundred works.