"Aid your brother whether he is the oppressor or the one being oppressed."
A man stated: "Oh Messenger of Allaah (sallallaahu alayhi wa sallam), I will help him when he is being oppressed, but how do I help him when he is the oppressor?"
The Messenger of Allaah (sallallaahu alayhi wa sallam) said:
"Prevent him from oppression and that's helping him."
The noble Shaykh Al Allaamah Muhammad ibn Saalih Al 'Uthaymeen (may Allaah have mercy upon him) stated about this narration in his explanation of Riyaadus Saaliheen #237:
"The helping (of your brother who is being oppressed) means to defend him from others. Meaning repelling that which harms him. Help your brother, meaning: repel from him that which harms him. This is the case whether he is an oppressor or one being oppressed. A man said: "Oh Messenger of Allaah, how do I help him when he is an oppressor?", he didn't say -I will not help him- rather he said: How do I help him?. He meant by his statement -I will help him, however inform me how am I to help him. The Prophet (sallallaahu alayhi wa sallam) said: "Prevent him and that is (considered) helping him." Therefore, if you see that this individual wants to transgress against the people, stop him and this is (considered) helping him. As for when the person is being oppressed, helping him is by way of repelling the oppressor away from him. In this narration there is evidence for the obligation of aiding the one who is oppressed and there is evidence for aiding the oppressor in the manner that has been mentioned by the Prophet (sallallaahu alayhi wa sallam)."
Sisters Upon Al-Istiqaamah