A believer is the mirror of his fellow believer
Abu Hurayrah (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said:
"A believer is the mirror of his fellow believer."
In this Hadih, the Prophet (may Allah's peace and blessings be upon him) gives a beautiful description and an eloquent simile of the attitude of a Muslim towards his Muslim brother. He outlines the responsibility of a Muslim towards his fellow Muslim; directs him to good manners so that he would adopt them and warns him against evil manners so that he would avoid them. He is thus like a polished mirror to his brother in which the latter sees his true self. The Hadīth indicates that giving advice to the believers is obligatory. If one becomes aware of a flaw in his Muslim brother, or an error that he commits, he should bring it to his attention and guide him to rectify it. But this should be done privately, because such advice in public is tantamount to disgrace.