In addition to one on one rape, Saudi preacher Muhammad al-Arifi also issued a fatwa allowing jihadi fighters to engage in “intercourse marriage” with captive Syrian women that lasts for a few hours “in order to give each fighter a turn”—also known as gang-rape.
Kuwaiti political activist, Salwa al-Mutairi is working to see the institution of sex-slavery return. She once asked Islam’s greatest authorities living in the city of Mecca, the city of Islam, about the legality of sex-slavery and how they all confirmed it to be perfectly legitimate. According to Mutairi:
A Muslim state must [first] attack a Christian state—sorry, I mean any non-Muslim state—and they [the women, the future sex-slaves] must be captives of the raid. Is this forbidden? Not at all; according to Islam, sex slaves are not at all forbidden. Quite the contrary, the rules regulating sex-slaves differ from those for free women [i.e., Muslim women]: the latter’s body must be covered entirely, except for her face and hands, whereas the sex-slave is kept naked from the bellybutton on up—she is different from the free woman; the free woman has to be married properly to her husband, but the sex-slave—he just buys her and that’s that.
I hope you read the sarcasm in my comment. I don't have a lot of words left to say about them. To me, what they are is apparent.