Exodus 34:16

34:16 and you then take ¹  his daughters for your sons, and when his daughters prostitute themselves to their gods, they will make your sons prostitute themselves to their gods as well.

Deuteronomy 7:3

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

¹ tn In the construction this verb would follow as a possible outcome of the last event, and so remain in the verbal sequence. If the people participate in the festivals of the land, then they will intermarry, and that could lead to further involvement with idolatry.