Jerome — as excerpted in the Catena Aurea on Matthew 5:38-42

“Mystically interpreted; When we are smitten on the right cheek, He said not, offer to him thy left, but the other; for the righteous has not a left. That is, if a heretic has smitten us in disputation, and would wound us in a right hand doctrine, let him be met with another testimony from Scripture.”