Deuteronomy 7:4

כי יסיר את בנך מאחרי FOR HE WILL TURN AWAY THY SON FROM FOLLOWING ME — i.e., the son of the heathen when he marries thy daughter, will turn away thy son (grandson) whom thy daughter will bear unto him from following Me. This teaches us, that thy daughter's son who is born of a heathen is termed thy son, but thy son’s son, who is born of a heathen woman, is not termed thy son, but her son, for, you see, in regard to the statement: “his daughter thou shalt not take [to thy son]" it does not add “For she will turn away thy son (grandson) from following Me" (Yevamot 23a).

כִּֽי־יָסִ֤יר אֶת־בִּנְךָ֙ מֵֽאַחֲרַ֔י וְעָבְד֖וּ אֱלֹהִ֣ים אֲחֵרִ֑ים וְחָרָ֤ה אַף־יְהֹוָה֙ בָּכֶ֔ם וְהִשְׁמִידְךָ֖ מַהֵֽר׃

For they will turn away thy son from following me, that they may serve other gods: so will the anger of the Lord be inflamed against you, and he will destroy thee speedily.