Genesis 42:12 (KJV)

And Joseph saw his brethren, and he knew them, but made himself strange unto them, and spake roughly unto them; and he said unto them, Whence come ye? And they said, From the land of Canaan to buy food.

And Joseph knew his brethren, but they knew not him.

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 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.