Numbers 31:17-21

Now therefore, kill every male among the little ones, and kill every woman who has known a man intimately.

However, all the girls who have not known a man intimately, keep alive for yourselves.

And as for you, camp outside the camp for seven days; whoever has killed a person and whoever has touched anyone killed, purify yourselves, you and your captives, on the third day and on the seventh day.

And you shall purify for yourselves every garment, every article of leather, every work of goats’ hair, and every article of wood.”

Then Eleazar the priest said to the men of war who had gone to battle, “This is the statute of the Law which the Lord has commanded Moses: