Commenting on Gal 1.8, Vincent of Lerins says:
“‘Even though an angel from heaven preach unto you any other Gospel than that which we have preached unto you, let him be accursed.’ It was not enough for the preservation of the faith once delivered to have referred to man; he must needs comprehend angels also. ‘Though we,’ he says, ‘or an angel from heaven.’ Not that the holy angels of heaven are now capable of sinning. But what he means is: Even if that were to happen which cannot happen, – if any one, be he who he may, attempt to alter the faith once for all delivered, let him be accursed.”
Vincent of Lerins , “A Commonitory For The Antiquity And Universality Of The Catholic Faith Against The Profane Novelties Of All Heresies,” in The Post-Nicene Fathers, ed. Philip Schaff, trans. C. A. Heurtley, electronic ed. (Garland, TX: Galaxie Software, 2000), 8.22.