Anas (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "Help your (Muslim) brother, whether he is an oppressor or oppressed." A man asked: "O Messenger of Allah! I will help the oppressed, but how can I help the oppressor?" The Prophet (peace and blessings be upon him) replied: "By preventing him from oppression, that is your helping him." Agreed upon.
Hadith Referenceمشكوة المصابيح / كتاب الآداب / 4957
Hadith Gradingالألبانی:مُتَّفَقٌ عَلَيْهِ | زبیر علی زئی:متفق عليه
Hadith Takhrij´تحقيق و تخريج: محدث العصر حافظ زبير على زئي رحمه الله` «متفق عليه، رواه البخاري (6952) و مسلم (2584/62)»