It was narrated from Anas bin Malik, that the Prophetﷺ said:

"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."

حَدَّثَنَا مُحَمَّدُ بْنُ حَاتِمٍ الْمُكْتِبُ، حَدَّثَنَا مُحَمَّدُ بْنُ عَبْدِ اللَّهِ الأَنْصَارِيُّ، حَدَّثَنَا حُمَيْدٌ الطَّوِيلُ، عَنْ أَنَسٍ، عَنِ النَّبِيِّ ﷺ قَالَ " انْصُرْ أَخَاكَ ظَالِمًا أَوْ مَظْلُومًا " . قُلْنَا يَا رَسُولَ اللَّهِ نَصَرْتُهُ مَظْلُومًا فَكَيْفَ أَنْصُرُهُ ظَالِمًا قَالَ " تَكُفُّهُ عَنِ الظُّلْمِ فَذَاكَ نَصْرُكَ إِيَّاهُ " . قَالَ وَفِي الْبَابِ عَنْ عَائِشَةَ .

قَالَ أَبُو عِيسَى هَذَا حَدِيثٌ حَسَنٌ صَحِيحٌ .