holy order from Moses, in the Book of Numbers, Chapter 31, Verses 13-18, as quoted from my 1985 translation by the Jewish Publication Society. The Israelites have just done a fairly pitiless job on the Midianites, slaughtering all of the adult males. But, says their stern commander-in-chief, they have still failed him:
Moses, Eleazer the priest, and all the chieftains of the community came out to meet them outside the camp. Moses became angry with the commanders of the army, the officers of thousands and the officers of hundreds, who had come back from the military campaign. Moses said to them, "You have spared every female! Yet they are the very ones who, at the bidding of Balaam, induced the Israelites to trespass against the Lord in the matter of Peor, so that the Lord's community was struck by the plague. Now, therefore, slay every male among the children, and slay also every young woman who has known a man carnally; but spare every young woman who has not had carnal relations with a man."