Matthew 18:15-16

15Jesus said, ‘If your Christian friend has done something wrong against you, you must go and speak to him. When you are alone with him, tell him what he has done that is wrong. He may agree with what you say. If he does, then you can call him your friend again.

16But maybe he does not want to listen to you. Then take one or two other people with you to speak to him. They will then know what wrong things your friend has done. Remember what the Bible says: “There must be two or three people to say certainly that another person has done something wrong. Two or three people must agree what has happened.”