Rashi on Exodus 6:14/רש"י על שמות ו׳:י״ד

1אלה ראשי בית אבתם THESE ARE THE HEADS OF THEIR FATHERS’ HOUSES — Since it (Scripture) finds itself compelled to give the genealogy of the tribe of Levi as far as Moses and Aaron because of Moses and Aaron, it begins to give the genealogy of the tribes in the order of their birth commencing from Reuben. And in Pesikta Rabbati 7 (on Numbers 7:12) I have seen the statement, that because their father Jacob reproached these three tribes in the hour of his death Scripture again enumerates here their genealogy alone of all the tribes to indicate that they nevertheless were men of worth.