Genesis 42:19
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: 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:
The verse belongs to Joseph's testing of his brothers after they came to Egypt to buy grain during the famine. The brothers insist they are honest men, explaining that they are twelve sons of one father, with the youngest still with their father and one brother gone. Joseph doubts their account and accuses them of spying, and the absence of Benjamin makes him wonder whether they have treated Benjamin as cruelly as they treated him.
The verse sets the terms for them to live and prove their truthfulness: one brother is to remain bound in prison while the others carry grain home for their famine-stricken households, and they must return with Benjamin to verify their claim and escape death. Joseph gives this condition while declaring that he fears God.
The release comes after three days of confinement, because Joseph is concerned that their father and families may be suffering for hunger. The release also reflects his conviction that their bitter sorrow and reflection on their past cruelty to him proves they have repented and will in no case treat Benjamin as they treated him. The brothers receiving these terms are mourning their wrong course. They know that failure to clear themselves of being spies means death or slavery. They fear God intends to punish them with slavery because they sold Joseph as a slave.
They accept the terms, though they fear and doubt that Jacob will let Benjamin go, since he believes Joseph suffered a cruel death. In fulfillment of the verse, Simeon is bound and kept behind in prison.