Numbers 31:18 in the King James Version
But all the women children, that have not known a man by lying with him, keep alive for yourselves.
Context
17 Now therefore kill every male among the little ones, and kill every woman who has known man by lying with him.
18 But all the girls, who have not known man by lying with him, keep alive for yourselves.
19 “Encamp outside of the camp for seven days. Whoever has killed any person, and whoever has touched any slain, purify yourselves on the third day and on the seventh day, you and your captives.