[Sahih Bukhari: Volume 3, Book 43, Number 622]
Narrated ‘Abdullah bin Umar (Radi Allah Anhu) : Allah’s Apostle (sal-allahu-alleihi-wasallam) said, “A Muslim is a brother of another Muslim, so he should not oppress him, nor should he hand him over to an oppressor. Whoever fulfilled the needs of his brother, Allah will fulfill his needs; whoever brought his (Muslim) brother out of a discomfort, Allah will bring him out of the discomforts of the Day of Resurrection, and whoever screened a Muslim, Allah will screen him on the Day of Resurrection.”

[Sahih Bukhari: Volume 3, Book 43, Number 624]
Narrated Anas (Radi Allah Anhu) : Allah’s Apostle (sal-allahu-alleihi-wasallam) 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.”

[Sahih Bukhari: Volume 3, Book 43, Number 629]
Narrated Abu Huraira (Radi Allah Anhu) : Allah’s Apostle (sal-allahu-alleihi-wasallam) said, “Whoever has oppressed another person concerning his reputation or anything else, he should beg him to forgive him before the Day of Resurrection when there will be no money (to compensate for wrong deeds), but if he has good deeds, those good deeds will be taken from him according to his oppression which he has done, and if he has no good deeds, the sins of the oppressed person will be loaded on him.”