Genesis 6:2

6:2 the sons of God saw that the daughters of humankind were beautiful. Thus they took wives for themselves from any they chose.

Deuteronomy 7:3-4

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.

Joshua 23:12-13

23:12 But if you ever turn away and make alliances with these nations that remain near you, and intermarry with them and establish friendly relations with them, 23:13 know for certain that the Lord our God will no longer drive out these nations from before you. They will trap and ensnare you; they will be a whip that tears your sides and thorns that blind your eyes until you disappear from this good land the Lord your God gave you.

Nehemiah 13:23-29

13:23 Also in those days I saw the men of Judah who had married women from Ashdod, Ammon, and Moab. 13:24 Half of their children spoke the language of Ashdod (or the language of one of the other peoples mentioned) and were unable to speak the language of Judah. 13:25 So I entered a complaint with them. I called down a curse on them, and I struck some of the men and pulled out their hair. I had them swear by God saying, “You will not marry off your daughters to their sons, and you will not take any of their daughters as wives for your sons or for yourselves! 13:26 Was it not because of things like these that King Solomon of Israel sinned? Among the many nations there was no king like him. He was loved by his God, and God made him king over all Israel. But the foreign wives made even him sin! 13:27 Should we then in your case hear that you do all this great evil, thereby being unfaithful to our God by marrying foreign wives?”

13:28 Now one of the sons of Joiada son of Eliashib the high priest was a son-in-law of Sanballat the Horonite. So I banished him from my sight.

13:29 Please remember them, O my God, because they have defiled the priesthood, the covenant of the priesthood, and the Levites.