'Swear by God' in the Bible

He also rebelled against King Nebuchadnezzar who had made him swear allegiance by God. He stiffened his neck and hardened his heart against turning to the Lord God of Israel.

So I contended with them and cursed them and struck some of them and pulled out their hair, and made them swear by God, saying, “You shall not give your daughters [in marriage] to their sons, nor take [any of] their daughters for your sons or for yourselves.