"Help your brother whether he is an oppressor or oppressed." It was said: "O Messenger of Allah! I help him when he is oppressed. But how can I help him when he oppresses?" He said: "Prevent him from oppression, that is your help for him." (Using translation from Tirmidhī 2255)
قَالَ رَسُولُ اللهِ ﷺ انْصُرْ أَخَاكَ ظَالِمًا أَوْ مَظْلُومًا قِيلَ يَا رَسُولَ اللهِ نَصَرْتُهُ مَظْلُومًا فَكَيْفَ أَنْصُرُهُ ظَالِمًا؟ قَالَ تَمْنَعُهُ مِنَ الظُّلْمِ فَذَلِكَ نَصْرُكَ إِيَّاهُ