Why the rapes of the Islamic State are Hallal

I have heard people who don't know about Islam comment that the Islamic State soldiers 'rape' women, and that this is against Islam.

This, however, is incorrect. These are not men committing rape, or if they are committing rape then Allah does not mind. Specifically, slaves are part of the booy (anfal) of jihad, and we know from the Prophet himself that Allah has no problem with men having sex with their female slaves. That is outlined clearly in the Qur'an, but also in this hadith:

Volume 7, Book 62, Number 137:

Narrated Abu Said Al-Khudri:

We got female captives in the war booty and we used to do coitus interruptus with them. So we asked Allah's Apostle about it and he said, "Do you really do that?" repeating the question thrice, "There is no soul that is destined to exist but will come into existence, till the Day of Resurrection."

 The Prophet had no problem at all with them men having sex with their new slaves. He was, however, troubles by their practice of coitus interruptus. For the life of me I wish more Muslims knew about the life of this man, because a lot of them would leave Islam and find a better man to follow.