(4) باب أَعِنْ أَخَاكَ ظَالِمًا أَوْ مَظْلُومًا
Narrated Anas:
Allah's Messenger (ﷺ) said, "Help your brother, whether he is an oppressor or he is an oppressed one. People asked, "O Allah's Messenger (ﷺ)! It is all right to help him if he is oppressed, but how should we help him if he is an oppressor?" The Prophet (ﷺ) said, "By preventing him from oppressing others."
Reference: Sahih al-Bukhari 2444
In-book reference: Book 46, Hadith 5
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 3, Book 43, Hadith 624