Genesis 44:10
And he said, Now also let it be according unto your words: he with whom it is found shall be my servant; and ye shall be blameless. And he said, Now also let it be according unto your words: he with whom it is found shall be my servant; and ye shall be blameless.
The silver cup was hidden in Benjamin's sack to gain further proof of the brothers when there was no other reason to hold them. When they were charged with repaying good with evil, they pointed to the money they had carried back from Canaan as proof that they would not steal silver or gold. In rash confidence they offered that the one with whom the cup was found should die and the rest should become slaves.
The steward softened that bargain and accepted it only in part, ruling that only the one with whom the cup was found would be kept as his servant or bondman, while the rest would be blameless and free to go. Under those terms the sacks were searched in order from oldest to youngest, and the cup was found in Benjamin's sack, leaving Benjamin liable to slavery. The brothers believed their own promise doomed Benjamin to slavery, leaving them speechless and tearing their clothes in grief, feeling God's hand against them for their past wickedness and fearing that Jacob's fears had come true, with dread over what this would mean for their father.