Genesis 42:16-19

16Send one of you, and let him bring your brother; and you shall be kept in prison, that your words may be tested to see whether there is any truth in you; or else, by the life of Pharaoh, surely you are spies!”

17So he put them all together in prison three days.

18Then Joseph said to them the third day, “Do this and live, for I fear God:

19If you are honest men, let one of your brothers be confined to your prison house; but you, go and carry grain for the famine of your houses.