Genesis 42:18-20

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.