Numbers 31:17-21

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 purify all your raiment, and all that is made of skins, and all work of goats’ hair, and all things made of wood.

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;