Isn’t it adultery when ISIS, Boko Haram, and others take sex slaves? I think they must have cut passages dealing with adultery out of their Qurans. But that is the way of "true believers" of any kind: their way is the only way, even if their texts say otherwise.
“The adulteress and the adulterer-whip each one of them a hundred lashes, and let no pity towards them overcome you regarding God's Law, if you believe in God and the Last Day. And let a group of believers witness their punishment.” Quran: 24:2 (The Light: an-Nur)
Excerpt From: Talal Itani. “Quran In English. Modern English Translation. Clear and Easy to Understand.” iBooks. https://itun.es/us/lvcp2.l
Also see "ISIS Committed Genocide Against Yazidis in Syria and Iraq, Panel Says"