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Criticism

Al-Razi's religious and philosophical views were later criticized by Abu Rayhan Biruni and Avicenna in the early 11th century. Biruni in particular wrote a short treatise (risala) dealing with al-Razi, criticizing him for his sympathy with Manichaeism, his Hermetical writings, his religious and philosophical views, for refusing to mathematize physics, and his active opposition to mathematics. Avicenna, who was himself a physician and philosopher, also criticized al-Razi. During a debate with Biruni, Avicenna stated:

Or from Muhammad ibn Zakariyya al-Razi, who meddles in metaphysics and exceeds his competence. He should have remained confined to surgery and to urine and stool testing —indeed he exposed himself and showed his ignorance in these matters.

Nasr-i-Khosraw posthumously accused him of having plagiarized Iranshahri, whom Khosraw considered the master of al-Razi.