Komentaryo sa Genesis 49:4: Rashi, Chizkuni, Da'at Zekenim & Ramban

פחז כמים The impetuosity and the precipitance with which you so hastily showed your wrath, just like water that rushes headlong in its course — therefore

כי עלית, “when you mounted;” “you desecrated Him Who is present even when I have intimate relations with my wife.” Yaakov accuses Reuven that as of the day when he invaded his privacy, he no longer had marital relations with Bilhah. Furthermore, when you desecrated my couch, you desecrated yourself and removed the sanctity of the kingship and the first-born status from yourself. Thus Jacob transferred the first-born status to Joseph. There are commentators who explained that Jacob said all of this to his other sons so that they should not wonder why he spoke so harshly to Reuven who had sinned gravely. The word עלה occurs in the sense of “departing, withdrawing its presence,” also in Psalms 102,25: על תעלני בחצי ימי, “do not take me away in the midst of my days.”

כי עלית על משכבי אביך, “you went up to your father’s bed;” On which occasion did this take place? At the time when Leah traded Yaakov’s turn to spend the night with Rachel for the mandrakes her son Reuven had found. (Genesis 30,15). (Br’eshit Rabbah 96.4)