Islamic State, IS, has written an article about sex slaves in their magazine Dabiq. Now apologists for Islam say that IS has nothing to do with Islam. But IS makes it very clear that when they capture Kafir women and rape them they are only doing what Mohammed did. They quote four verses in the Koran about how Kafir women can be captured and used for sex. Mohammed had sex slaves and his closest companions had sex slaves.
Islamic State reminds Muslims that one of the benefits of sex slavery is that they convert to Islam to gain their freedom and produce Muslim children.
Islamic State is pure Islam.