Jami` at-Tirmidhi 2255
جامع الترمذي#2255SahihIt was narrated from Anas bin Malik, that the Prophet(s.a.w) 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
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Ahmad Muhammad ShakirSahih
Al-AlbaniSahih
Bashar Awad MaaroufHasan Sahih
Zubair Ali ZaiSahih
In-book reference: 33:98