John Chrysostom — as excerpted in the Catena Aurea on Matthew 18:15-17

“Yet the Lord enjoins nothing of this sort to be observed towards those who are without the Church, such as He does in reproving a brother. Of those that are without He says. If any smite thee on the one cheek, offer to him the other also. (Mat. 5:39.) as Paul speaks, What have I to do to judge them that are without? (1 Cor. 5:12.) But brethren he bids us reprove, and turn away from.”