John Lightfoot on Luke 17:3

[Rebuke him.] The Rabbins are not sparing in granting the lawfulness of repeating rebuke upon rebuke, but they are most sparing about forgiveness where any hath given an offence. They allow, from Leviticus 19:17, that a man may rebuke a hundred times if there be any need for it; nay, that it is the duty of a disciple to rebuke his master if occasion be. But as to forgiving him that offends, they abuse the words of the prophet, Amos 1:2, "for three transgressions"; and that of Job 33:29, "Lo, God worketh all these things three times with man"; and teach that a man is not bound to forgive a fourth trespass.