Sayyiduna Anas bin Malik (may Allah be pleased with him) narrates this statement of the Noble Prophet (peace and blessings be upon him): "Help your brother, whether he is an oppressor or oppressed." The people said: O Messenger of Allah (peace and blessings be upon him)! We help the oppressed, but how do we help the oppressor? The Noble Prophet (peace and blessings be upon him) said: Stop him from oppression.
Hadith Referenceصحیح ابن حبان / كتاب الغصب / 5167
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح - «الإرواء» (8/ 97)، «الروض النضير» (32): ق.فضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده صحيح على شرط مسلم