Deuteronomy 6:13 in the King James Version
Thou shalt fear the LORD thy God, and serve him, and shalt swear by his name.
Context
12 then beware lest you forget the LORD, who brought you out of the land of Egypt, out of the house of bondage.
13 You shall fear the LORD your God; and you shall serve him, and shall swear by his name.
14 You shall not go after other gods, of the gods of the peoples who are around you,