He calls Cepha [=a rock];
not the person of Simon, but the confession and the right faith that were in
him, which the Fathers had caused to flow into his mouth, which [confession] is
incorruptible and immoveable for ever. (The Commentaries of Isho'dad of Merv,
3 vols. [trans. Margaret Dunlop Gibson; Cambridge: Cambridge University Press,
1911], 1:66)