Their only difficulty was how to distinguish the heretics from the orthodox: "Slay them all," said the abbot of Citeaux; "the Lord will know his own."

as quoted in Caesarius of Heisterbach, Dialogus miraculorum, bk. v, ch. 21. . . . . Caedite eos; novi enim Dominus qui sunt ejus. Reported in Jules Michelet, History of France, tr. G. H. Smith (New York, 1882), vol. i, p. 280