What the United Nations community regards as senseless acts of horrific violence are to ISIS’s acolytes part of an exalted campaign of purification through sacrificial killing and self-immolation: Know that Paradise lies under the shade of swords, says a hadith, or saying of the Prophet; this one comes from the Sahih al-Bukhari, a collection of the Prophet’s sayings considered second only to the Qu’ran in authenticity and is now a motto of ISIS fighters.