Deuteronomy 7:2-4

New Century Version

² The Lord your God will hand these nations over to you, and when you defeat them, you must destroy them completely. Do not make a peace treaty with them or show them any mercy. ³ Do not marry any of them, or let your daughters marry their sons, or let your sons marry their daughters. ⁴ If you do, those people will turn your children away from me, to begin serving other gods. Then the Lord will be very angry with you, and he will quickly destroy you.