Genesis 42:14-20

But Joseph insisted, “As I said, you are spies! This is how I will test your story. I swear by the life of Pharaoh that you will never leave Egypt unless your youngest brother comes here! One of you must go and get your brother. I’ll keep the rest of you here in prison. Then we’ll find out whether or not your story is true. By the life of Pharaoh, if it turns out that you don’t have a younger brother, then I’ll know you are spies.” So Joseph put them all in prison for three days. On the third day Joseph said to them, “I am a God-fearing man. If you do as I say, you will live. If you really are honest men, choose one of your brothers to remain in prison. The rest of you may go home with grain for your starving families. But you must bring your youngest brother back to me. This will prove that you are telling the truth, and you will not die.” To this they agreed.