Genesis 42:24

And he turned himself about from them, and wept at this evidence of their complete change of heart; and returned to them again, and communed with them, and took from them Simeon, and bound him before their eyes. He spared Reuben, either because he did not want to harm the right of the firstborn, or because Reuben was less guilty than some of the rest. His object had been attained, he had the information which he sought.