Bible Verses About Oaths: Custom of swearing by the life of the king

Here's how you can prove you're not lying: as Pharaoh lives, you will not leave here unless your youngest brother comes here.

Send one of you, and let him bring your brother. Meanwhile, you will be kept in custody. This will prove whether there is any truth in what you say. Otherwise, as Pharaoh lives, you are certainly spies."