Commentaire sur La Genèse 37:29

וישב ראובן AND REUBEN RETURNED — When he (Joseph) was sold he had not been present, for it was his day (his turn) to go to attend to his father (Genesis Rabbah 84:19). Another explanation is: he had not sat with them at the meal because he was occupied with his sack-cloth and fast in penitence for having disturbed his father’s couch (Genesis Rabbah 84:19).

וישב ראובן אל הבור, Reuben returned to the pit, etc. What was Reuben's argument when he complained to the brothers ואני אנה אני בא, "where shall I go?" Would Joseph not have been lost even if his own suggestion to throw him into a pit had been carried out? After all, the Torah itself testified that Reuben had never told his brothers that he intended to save Joseph and to restore him to his father! When Yehudah said to the other brothers: "what profit is there in killing our brother, etc," does this not prove that Joseph's remaining in the pit was meant to result in his death? How then could Reuben complain to his brothers?

וישב, he returned from wherever he had gone to his brothers, going back to the pit to see if he could rescue Joseph without his brothers finding out, and to return him to his father. There is a discussion in Bereshit Rabbah 84,19 as to where Reuven had been in the interval. According to some, it had been his turn to attend to the needs of his father, whereas according to Rabbi Eliezer he was engaged in doing penance, etc., for having slept with Bilhah, his father’s concubine.