Sforno on Genesis 49:4/ספורנו על בראשית מ״ט:ד׳

1אז חללת יצועי עלה, at that time you defiled your father’s dignity. Alternatively, Yaakov may have referred to Reuven’s act being a desecration of G’d’s honour. As an appropriate punishment, Reuven’s own status, which had been one of special honour, would be diminished accordingly.