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Samples followed by the link to the rest.
Arnaud (or Arnau) Amalric (died 1225) was a Cistercian church leader who took a prominent role in the Albigensian Crusade. He is remembered for allegedly giving advice to a soldier wondering how to distinguish the Catholic friendlies from the Cathar enemies to just “Kill them all. For the Lord knows them that are His.”
Caedite eos. Novit enim Dominus qui sunt eius (Kill them all. For the Lord knoweth them that are His.)
This is the origin of the modern phrase, “Kill them all and let God sort them out.”