Sunan At-Tirmidhi

It was narrated from Anas bin Malik, that the Prophet(s.a.w) said:""Help your brother whether he is an oppressor or oppressed."" It was said: ""O Messenger of Allah! I help him when he is oppressed. But how can I help him when he oppresses?"" He said: ""Prevent him from oppression, that is your help for him