Matthew 18:15-17, 20

“If your fellow believer sins against you, go and tell him in private what he did wrong. If he listens to you, you have helped that person to be your brother or sister again. But if he refuses to listen, go to him again and take one or two other people with you. ‘Every case may be proved by two or three witnesses.’ If he refuses to listen to them, tell the church. If he refuses to listen to the church, then treat him like a person who does not believe in God or like a tax collector.

This is true because if two or three people come together in my name, I am there with them.”