Where did they get the idea for this? You guessed it:

“And know that anything you obtain of war booty – then indeed, for Allah is one fifth of it and for the Messenger and for near relatives and the orphans, the needy, and the traveler, if you have believed in Allah and in that which We sent down to Our Servant on the day of criterion – the day when the two armies met. And Allah, over all things, is competent.” (Qur’an 8:41)

The Islamic State believes that the world’s Muslims are at war with the world’s non-Muslims, and are thus entitled to the spoils of war, of which a fifth belongs to them as the caliphate, the sole legitimate government for Muslims.

And of course the Infidels’ wealth and property belongs to the Muslims by right, for the Qur’an specofoes that Muslims must fight them until the “pay the jizya with willing submission and feel themselves subdued” (Qur’an 9:29). So the Infidels paying for the upkeep of the Muslims is the natural order of things.

“ISIS Tells Muslims to Go Steal, Send the Caliphate 20 Percent of the Loot,” by Bridget Johnson, PJ Media, April 5, 2017: