Deuteronomy 7:2-4

New Revised Standard Version Catholic Edition

² and when the Lord your God gives them over to you and you defeat them, then you must utterly destroy them. Make no covenant with them and show them no mercy. ³ Do not intermarry with them, giving your daughters to their sons or taking their daughters for your sons, ⁴ for that would turn away your children from following me, to serve other gods. Then the anger of the Lord would be kindled against you, and he would destroy you quickly.