It was narrated from Abu Hurairah that the Messenger of Allah P.B.U.H: "The adultere, at the time he is committing the adultury, is not a believer; at the time he is ,he is not a believer; the thief at the time he is stealing, is not a believer; the plunderer, at the time he is plundering wIth the people looking on, is not a believer.'' (Sahih)