Deuteronomy 21:10-13

10When you go to war against your enemies and the LORD your God delivers them into your hand and you take them captive, 11if you see a beautiful woman among them, and you desire her and want to take her as your wife, 12then you shall bring her into your house. She must shave her head, trim her nails, 13and put aside the clothing of her captivity.

After she has lived in your house a full month and mourned her father and mother, you may have relations with her and be her husband, and she shall be your wife.