Exodus 34:16
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.

Deuteronomy 7:3
Do not intermarry with them. Do not give your daughters to their sons or take their daughters for your sons,

Ezra 9:1-3, 12-14
After these things had been accomplished, the leaders approached me and said: "The people of Israel, including the priests and Levites, have not kept themselves separate from the surrounding peoples whose abominations are like those of the Canaanites, Hittites, Perizzites, Jebusites, Ammonites, Moabites, Egyptians, and Amorites. . . .

Ezra 10:10-12
Then Ezra the priest stood up and said to them, "You have been unfaithful by marrying foreign women, adding to the guilt of Israel. . . .