Deuteronomy 10:20

20 Fear the LORD your God and serve him. Hold fast to him and take your oaths in his name.

Read Deuteronomy 10:20 Using Other Translations

Thou shalt fear the LORD thy God; him shalt thou serve, and to him shalt thou cleave, and swear by his name.
You shall fear the LORD your God. You shall serve him and hold fast to him, and by his name you shall swear.
You must fear the LORD your God and worship him and cling to him. Your oaths must be in his name alone.