Anas (R.A) reported: Messenger of Allah (peace be upon him) said, “Help your brother, whether he is an oppressor or is oppressed”. A man enquired: “O Messenger of Allah (peace be upon him)! I help him when he is oppressed, but how can I help him when he is an oppressor?” He (peace be upon him) said, “You can keep him from committing oppression. That will be your help to him”.
Riyad as-Salihin, Book 1, Hadith 237
