Sayyiduna Abu Hurairah, may Allah be pleased with him, narrates that the Prophet Muhammad, peace and blessings be upon him, said: "The person who commits adultery is not a believer while committing adultery, the person who steals is not a believer while stealing, the person who drinks alcohol is not a believer while drinking alcohol, the person who commits robbery—who robs someone of something valuable while Muslims are watching him—is not a believer while committing robbery."
The narrator says: I asked Zuhri: What does this mean? He replied: It was obligatory upon the Prophet Muhammad, peace and blessings be upon him, to convey it, and it is obligatory upon us to accept it.