"You shall certainly rebuke your neighbor"Leviticus 19:17.

We are commanded to verbally rebuke a fellow Jew who has sinned, and to rebuke and attempt to prevent an individual who is about to sin. This commandment applies to everyone, even if the one who has sinned (or is about to sin) is a great individual. To say, "I shall not sin; what another does is G‑d's concern," is contrary to the Torah's viewpoint. And if the first rebuke has not accomplished its goal, we must do so again and again. We must be careful, however, to rebuke in a pleasant manner—not to embarrass our fellow, G‑d forbid.

Included in this commandment is the obligation to rebuke someone who has wronged you, as opposed to silently harboring a grudge against that individual.