And all married women (are forbidden unto you) save those (captives) whom your right hands possess. It is a decree of Allah for you. Lawful unto you are all beyond those mentioned, so that ye seek them with your wealth in honest wedlock, not debauchery. And those of whom ye seek content (by marrying them), give unto them their portions as a duty. And there is no sin for you in what ye do by mutual agreement after the duty (hath been done). Lo! Allah is ever Knower, Wise.
The pertinent part of the verse:
And all married women (are forbidden unto you) save those (captives) whom your right hands possess.
So married women are forbidden. But the verse then says except those women you own as slaves. So, married slave women are not forbidden to Muslim captors. Otherwise, relationships with married women who are not your slave are strictly forbidden.
Hmmm.