Musar zu Bereschit 37:22

(Ibid. 42:37): "And Reuven said to his father: 'You may kill my two sons if I do not bring him [Benjamin] back to you… (38): And he said: 'My son shall not go down with you.'" The Midrash relates that Yaakov said about him [Reuven]: "He is a foolish bechor [(first-born)]. Are they his sons and not my sons?" The words of Reuven must, indeed, be understood, but, essentially, this is the explanation: Whatever issues from a man's mouth [(aside from what relates to fear of the L-rd, which is a function of man's free will)] is brought about by Heaven. This is the thrust of Chazal's statement: "All is in the hands of Heaven except the fear of Heaven." And the Midrash tells us that this ejaculation of Reuven's [("You may kill my two sons, etc.")] was fulfilled in his sons, [i.e., descendants], Dathan and Aviram [(in the episode of Korach)]. And, in truth, he [Reuven] himself was the cause of this, by saying (Bereshith 27:32): "Cast him into this pit which is in the desert." The act was extremely evil, for which reason they [Dathan and Aviram] descended, living, to Sheol, to the midst of the pit. As to his intent, being good, as it is written (Bereshith, Ibid.): "in order to rescue him from their hands to return him to his father," he merited that one of his descendants, On ben Peleth, be saved, by returning in repentance to His Father in heaven (wherefore he was called "On," his being in aninuth ["mourning" (for his sin)] all of his life, as Chazal have stated.