Numbers 31:20 (KJV)

And Moses said unto them, Have ye saved all the women alive?

Behold, these caused the children of Israel, through the counsel of Balaam, to commit trespass against the LORD in the matter of Peor, and there was a plague among the congregation of the LORD.

Now therefore kill every male among the little ones, and kill every woman that hath known man by lying with him.

But all the women children, that have not known a man by lying with him, keep alive for yourselves.

And do ye abide without the camp seven days: whosoever hath killed any person, and whosoever hath touched any slain, purify both yourselves and your captives on the third day, and on the seventh day.

And Eleazar the priest said unto the men of war which went to the battle, This is the ordinance of the law which the LORD commanded Moses;

Only the gold, and the silver, the brass, the iron, the tin, and the lead,

Every thing that may abide the fire, ye shall make it go through the fire, and it shall be clean: nevertheless it shall be purified with the water of separation: and all that abideth not the fire ye shall make go through the water.

And ye shall wash your clothes on the seventh day, and ye shall be clean, and afterward ye shall come into the camp.

And the LORD spake unto Moses, saying,