Matthew 18:17

17 If your friend still will not agree that he has done something wrong, then go and tell the church leaders. If he does not agree with the leaders, stop being his friend. He is like somebody who refuses to obey God.

18:17The word ‘church’ means a group of Christians. They meet together because they are obeying Jesus. It does not mean the building where they meet.
18:17This does not mean that we should only be friends with other Christians. We can be friends with other people too. But perhaps a person says that he follows Jesus. But he does not obey Jesus. Then we should not be a special friend of that person.