Genesis 42:18 (KJV)

And they said, Thy servants are twelve brethren, the sons of one man in the land of Canaan; and, behold, the youngest is this day with our father, and one is not.

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 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.

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:

But bring your youngest brother unto me; so shall your words be verified, and ye shall not die. And they did so.

And they said one to another, We are verily guilty concerning our brother, in that we saw the anguish of his soul, when he besought us, and we would not hear; therefore is this distress come upon us.

And Reuben answered them, saying, Spake I not unto you, saying, Do not sin against the child; and ye would not hear? therefore, behold, also his blood is required.

And they knew not that Joseph understood them; for he spake unto them by an interpreter.