Kill 'em all, and let god sort 'em out.

Sadly, it seems that this disgusting phrase has a historical basis.

Albigensian Crusade

In the bloodiest incident of the war, in 1209, perhaps 10,000 of the inhabitants of Béziers [ed: France] were slaughtered during the storming of the city by the Catholic forces headed by Simon de Montfort. In a famous legend relating to this incident, the Papal legate, Arnaud-Amaury, the Abbot of Citeaux, was asked how to distinguish between the Catholic and Cathars, and allegedly answered, "Kill them all, God will know his own". The Catholic Encyclopedia denies these words were ever spoken, although they were recorded soon after the event by a respected Church chronicler who was also Arnaud-Amaury's fellow Cistercian. They are also consistent with other sources such as the contemporary Song of the Crusade.