Genesis 42:15-19

Hereby ye shall be proved: By the life of Pharaoh ye shall not go forth hence, except your youngest brother come hither.

Send one of you, and let him fetch your brother, and ye shall be kept in prison, that your words may be proved, whether there be any truth in you: or else by the life of Pharaoh surely ye are spies.

And he put them all together into ward three days.

And Joseph said unto them the third day, This do, and live; for I fear God:

If ye be true men, let one of your brethren be bound in the house of your prison: go ye, carry corn for the famine of your houses: