Deuteronomy 7:2-4

7:2 and he delivers them over to you and you attack them, you must utterly annihilate them. Make no treaty with them and show them no mercy! 7:3 You must not intermarry with them. Do not give your daughters to their sons or take their daughters for your sons, 7:4 for they will turn your sons away from me to worship other gods. Then the anger of the Lord will erupt against you and he will quickly destroy you.