Early Byzantine polemic concluded Muhammad’s God is a devil rather than the true God

Evidence

Nicetas seems to argue in one chapter that Muhammad’s ‘admission’ of some things out of Scripture implies acceptance of Scripture, and that since he also asserts different things of his own invention of the same God, he makes God either not to exist or to be changeable; the God he speaks of does not accept the Christian Law, and so cannot be the true God; it follows that the God of Muhammad is really a devil. — Norman Daniel, Islam and the West, 59