Genesis 42:14-20

But Joseph said to them, “I can see I was right! You are spies! But I will give you a way to prove you are telling the truth. As surely as the king lives, you will not leave this place until your youngest brother comes here. One of you must go and get your brother. The rest of you will stay here in prison. We will see if you are telling the truth. If not, as surely as the king lives, you are spies.” Then Joseph put them all in prison for three days. On the third day Joseph said to them, “I am a God-fearing man. Do this and I will let you live: If you are honest men, let one of your brothers stay here in prison while the rest of you go and carry grain back to feed your hungry families. Then bring your youngest brother back here to me. If you do this, I will know you are telling the truth, and you will not die.” The brothers agreed to this.