سورة An-Noor ( The Light ) - الآية 3

The adulterer marries not but an adulteress or a Mushrikah and the adulteress none marries her except an adulterer or a Muskrik [and that means that the man who agrees to marry (have a sexual relation with) a Mushrikah (female polytheist, pagan or idolatress) or a prostitute, then surely he is either an adulterer, or a Mushrik (polytheist, pagan or idolater, etc.) And the woman who agrees to marry (have a sexual relation with) a Mushrik (polytheist, pagan or idolater) or an adulterer, then she is either a prostitute or a Mushrikah (female polytheist, pagan, or idolatress, etc.)]. Such a thing is forbidden to the believers (of Islamic Monotheism).