Midrash su Genesi 49:19

Gad, a troop shall troop upon him; but he shall troop at the end (Gen. 49:19). That is to say, the redeemer who will come at the end of days will descend from Gad, for he was one of the last to come: Behold, I will send you Elijah the prophet before the coming of the great and terrible day of the Lord (Mal. 3:23). And Elijah descended from Gad. Hence it is said: But he shall troop in the end.