Genesis 42:9-12, 14-17, 19-20

And Joseph remembered the dreams which he dreamed of them, and said unto them, Ye are spies; to see the nakedness of the land ye are come. And they said unto him, Nay, my lord, but to buy food are thy servants come. We are all one man’s sons; we are true men, thy servants are no spies. And he said unto them, Nay, but to see the nakedness of the land ye are come.

And Joseph said unto them, That is it that I spake unto you, saying, Ye are spies: 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 bound, that your words may be proved, whether there be truth in you: or else by the life of Pharaoh surely ye are spies. And he put them all together into ward three days.

if ye be true men, let one of your brethren be bound in your prison-house; but go ye, carry grain for the famine of your houses: and bring your youngest brother unto me; so shall your words be verified, and ye shall not die. And they did so.