Phrase coined by Ali G - the ironically white, Cambridge educated comedian who has made a really successful career out of his TV persona/s. Ali G is actually called Sasha Baron Cohen and is not a Muslim. The phrase follows his screen belief that he is a black gangster from Staines (England).
Police officer: Can you please move back to the side sir or we will have to take you to the station?
Ali G: Wait a minute, come on, is it because I is black?