Anas ibn Mālik (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "None of you is a real believer until he loves for his brother what he loves for himself.''
A real believer should love for his Muslim brother what he loves for himself, i.e. to support one's brother in every thing that is useful to him, whether it is related to religious or life affairs, i.e. giving him advice, commanding his to do the right, forbidding him from doing the wrong, and guiding him to everything that one might like for oneself. Meanwhile, a Muslim should keep his Muslim brother safe from every hateful and harmful thing.