Masood Bin Tariq

Narrated by Anas Razi Allah o anhu that Muhammad (saw) said,
"Help your brother, whether he is an oppressor or he is an oppressed one. People asked, "O Allah's Apostle! It is all right to help him if he is oppressed, but how should we help him if he is an oppressor?" The Prophet said, "By preventing him from oppressing others."
Bukhari. Book of Oppression # 1116