Rashi on Genesis 42:38/רש"י על בראשית מ״ב:ל״ח

1לא ירד בני עמכם MY SON SHALL NOT GO DOWN WITH YOU — He did not accept Reuben’s offer. He said, “What a fool is this oldest son of mine! He suggests that I should kill his sons. Are they his only and not mine also?” (Genesis Rabbah 91:9)