Mukhtasar Bukhari

Narrated Anas (may Allah be pleased with him): The Messenger of Allah (peace and blessings of Allah be upon him) said: "Help your brother, whether he is an oppressor or is oppressed." The Companions (may Allah be pleased with them) said, "O Messenger of Allah! We understand how to help the oppressed, but how should we help the oppressor?" He (peace be upon him) said: "By holding his hand." (i.e., by preventing him from committing oppression).