1 Kings 18:10

18:10 As certainly as the Lord your God lives, my master has sent to every nation and kingdom in an effort to find you. When they say, ‘He’s not here,’ he makes them swear an oath that they could not find you.

Hebrews 6:16-17

6:16 For people swear by something greater than themselves, and the oath serves as a confirmation to end all dispute. 6:17 In the same way God wanted to demonstrate more clearly to the heirs of the promise that his purpose was unchangeable, and so he intervened with an oath,