Concerning the Nature of Good, Against the Manichaeans

Wherefore neither can God's nature suffer harm, nor can any nature under God suffer harm unjustly: for when by sinning unjustly some do harm, an unjust will is imputed to them; but the power by which they are permitted to do harm is from God alone, who knows, while they themselves are ignorant, what they ought to suffer, whom He permits them to harm.