Nehemiah 13:23-27
In those days I also saw Jews who had married women from Ashdod, Ammon, and Moab. / Half of their children spoke the language of Ashdod or of the other peoples, but could not speak the language of Judah. / I rebuked them and called down curses on them. I beat some of these men and pulled out their hair. Then I made them take an oath before God and said, “You must not give your daughters in marriage to their sons or take their daughters as wives for your sons or for yourselves! ...

Malachi 2:11-12
Judah has broken faith; an abomination has been committed in Israel and in Jerusalem. For Judah has profaned the LORD’s beloved sanctuary by marrying the daughter of a foreign god. / As for the man who does this, may the LORD cut off from the tents of Jacob everyone who is awake and aware—even if he brings an offering to the LORD of Hosts.

Deuteronomy 7:3-4
Do not intermarry with them. Do not give your daughters to their sons or take their daughters for your sons, / because they will turn your sons away from following Me to serve other gods. Then the anger of the LORD will burn against you, and He will swiftly destroy you.

1 Kings 11:1-2
King Solomon, however, loved many foreign women along with the daughter of Pharaoh—women of Moab, Ammon, Edom, and Sidon, as well as Hittite women. / These women were from the nations about which the LORD had told the Israelites, “You must not intermarry with them, for surely they will turn your hearts after their gods.” Yet Solomon clung to these women in love.

Exodus 34:15-16
Do not make a covenant with the inhabitants of the land, for when they prostitute themselves to their gods and sacrifice to them, they will invite you, and you will eat their sacrifices. / And when you take some of their daughters as brides for your sons, their daughters will prostitute themselves to their gods and cause your sons to do the same.

2 Corinthians 6:14-17
Do not be unequally yoked with unbelievers. For what partnership can righteousness have with wickedness? Or what fellowship does light have with darkness? / What harmony is there between Christ and Belial? Or what does a believer have in common with an unbeliever? / What agreement can exist between the temple of God and idols? For we are the temple of the living God. As God has said: “I will dwell with them and walk among them, and I will be their God, and they will be My people.” ...

1 Corinthians 7:12-14
To the rest I say this (I, not the Lord): If a brother has an unbelieving wife and she is willing to live with him, he must not divorce her. / And if a woman has an unbelieving husband and he is willing to live with her, she must not divorce him. / For the unbelieving husband is sanctified through his believing wife, and the unbelieving wife is sanctified through her believing husband. Otherwise your children would be unclean, but now they are holy.

Judges 3:5-6
Thus the Israelites continued to live among the Canaanites, Hittites, Amorites, Perizzites, Hivites, and Jebusites. / And they took the daughters of these people in marriage, gave their own daughters to their sons, and served their gods.

Nehemiah 10:30
We will not give our daughters in marriage to the people of the land, and we will not take their daughters for our sons.

1 Kings 16:31
And as if it were not enough for him to walk in the sins of Jeroboam son of Nebat, he even married Jezebel the daughter of Ethbaal king of the Sidonians, and he then proceeded to serve and worship Baal.

2 Kings 17:33-34
They worshiped the LORD, but they also served their own gods according to the customs of the nations from which they had been carried away. / To this day they are still practicing their former customs. None of them worship the LORD or observe the statutes, ordinances, laws, and commandments that the LORD gave the descendants of Jacob, whom He named Israel.

2 Chronicles 21:6
And Jehoram walked in the ways of the kings of Israel, just as the house of Ahab had done. For he married a daughter of Ahab and did evil in the sight of the LORD.

2 Chronicles 19:2
Jehu son of Hanani the seer went out to confront him and said to King Jehoshaphat, “Should you help the wicked and love those who hate the LORD? Because of this, the wrath of the LORD is upon you.

1 Corinthians 5:9-11
I wrote you in my letter not to associate with sexually immoral people. / I was not including the sexually immoral of this world, or the greedy and swindlers, or idolaters. In that case you would have to leave this world. / But now I am writing you not to associate with anyone who claims to be a brother but is sexually immoral or greedy, an idolater or a verbal abuser, a drunkard or a swindler. With such a man do not even eat.

Ephesians 5:11
Have no fellowship with the fruitless deeds of darkness, but rather expose them.