Lactantius

“ Therefore ofttimes having uttered the greatest howlings, they cry out that they are beaten, and are on fire, and that they are just on the point of coming forth: so much power has the knowledge of God, and righteousness! Whom, therefore, can they injure, except those whom they have in their own power? In short, Hermes affirms that those who have known God are not only safe from the attacks of demons, but that they are not even bound by fate. “The only protection,” he says, “is piety, for over a pious man neither evil demon nor fate has any power: for God rescues the pious man from all evil ”

“ And what piety is, he testifies in another place, in these words: “For piety is the knowledge of God.” Asclepius also, his disciple, more fully expressed the same sentiment in that finished discourse which he wrote to the king. ”

“ XVI.—That Demons Have No Power Over Those Who are Established in the Faith.
And the nature of all these deceits [1] is obscure to those who are without the truth. For they think that those demons profit them when they cease to injure, whereas they have no power except to injure. [2] Some one may perchance say that they are therefore to be worshipped, that they may not injure, since they have the power to injure. ”