Matthew 18:15-17

15 "Moreover, if your brother commits a sin against you, go and show him his fault -- but privately, just between the two of you. If he listens to you, you have won back your brother.

16 If he doesn't listen, take one or two others with you so that every accusation can be supported by the testimony of two or three witnesses.l

17 If he refuses to hear them, tell the congregation; and if he refuses to listen even to the congregation, treat him as you would a pagan or a tax-collector.