Deuteronomy 7:3 in the King James Version
Neither shalt thou make marriages with them; thy daughter thou shalt not give unto his son, nor his daughter shalt thou take unto thy son.
Context
2 and when the LORD your God delivers them up before you, and you strike them, then you shall utterly destroy them. You shall make no covenant with them, nor show mercy to them.
3 You shall not make marriages with them. You shall not give your daughter to his son, nor shall you take his daughter for your son.
4 For that would turn away your sons from following me, that they may serve other gods. So the LORD’s anger would be kindled against you, and he would destroy you quickly.