Midrasz do Kapłańska 9:21

13) (Vayikra 9:18): "And he slaughtered the ox and the ram, the sacrifice of the peace-offerings, which was the people's": From here we learn of peace-offerings. (Vayikra 9:21): "And the breasts and the right thigh Aaron waved as a wave-offering before the L–rd": To teach us the greatness of Aaron and of his sons — that in a brief time they mastered seven (sacrificial) services: slaughtering, receiving (of the blood), dashing, sprinkling, purification, spilling and waving.