Incidentally, before we scream blue murder at Islam for this .... let's read the Christian Bible (the Word of God, in exactly the same way as the Koran, according to some)

(Deuteronomy 22:23-24 NAB)

If within the city a man comes upon a maiden who is betrothed, and has relations with her, you shall bring them both out of the gate of the city and there stone them to death: the girl because she did not cry out for help though she was in the city, and the man because he violated his neighbors wife.