Rashi on Numbers 7:23/רש"י על במדבר ז׳:כ״ג

1ולזבח השלמים בקר שנים AND FOR A SACRIFICE OF PEACE-OFFERINGS TWO OXEN — The two peace-offerings are an allusion to Moses and Aaron who made peace between Israel and their Father in Heaven (Numbers Rabbah 13:19).

2אילם כבשים ועתדים — three species — in allusion to the three divisions of the nation: priests, Levites and ordinary Israelites, and also in allusion to the Pentateuch, the Prophets and the Hagiographa, the three sections of the Holy Scriptures. There are three times “five”, in allusion to the “Five Books of Moses”, to the five Commandments written on one of the Tablets and to the five written on the other (Numbers Rabbah 14:10). Thus far have I found in the work of R. Moshe the Preacher.