Sforno on Genesis 35:23/ספורנו על בראשית ל״ה:כ״ג

1בכור יעקב ראובן, as far as Heaven was concerned Reuven did not suffer consequences because he had repented forthwith. He also did not suffer really in this world, i.e. on earth, until on his deathbed Yaakov punished him by depriving him of the material benefits enjoyed by the first born in that he inherits an extra share of his father’s estate. This punishment was withheld in accordance with the principle that anyone guilty of being ostracised by the community is not actually ostracised until the leading sage of the generation declares him to be so. (Moed Katan 16) This is based on Judges 5,23 where Devorah, the ruling judge of Israel, curses the inhabitants of a certain place called מרוז who had failed to answer her call to arms against the army of Siserah, general of Yavin, King of the Canaanites who had been oppressing the Israelites. The מלאך ה' she quotes in that verse is the leader of the generation, herself in this instance.