1 Peter 3:9

not rendering evil for evil, or reviling for reviling; but contrariwise blessing; for hereunto were ye called, that ye should inherit a blessing.

Rendering evil for evil ... This, of course, was an accepted ethic of paganism; but it is rejected by Christians. "Recompense to no man evil for evil" (Romans 12:17). "See that none render evil for evil unto any man" (1 Thessalonians 5:15). This was not an ethic developed by the apostles, but one handed down directly from the mouth of the Lord himself, who said, "Love your enemies, do good to them that hate you, bless them that curse you, and pray for them which despitefully use you" (Luke 6:27,28). Likewise, all of the apostolic teachings should be understood to have originated, not with themselves, but with the Lord Jesus Christ.