"Moses and Aaron in their priesthood. Rabbi Yudan, in the name of Rabbi Yossi son of Rabbi Judah, and Rabbi Berachiah in the name of Rabbi Yehoshua ben Korcha said, 'During the forty years that Israel was in the wilderness, Moses never refrained from serving as high priest, as it is said, "Moses and Aaron in their priesthood." Rabbi Berachiah said in the name of Rabbi Simon, 'It is a full verse (1 Chronicles 23:13-14): "The sons of Amram: Moses and Aaron.
And Aaron was set apart to sanctify him as most holy, he and his sons forever, to offer the bread of the presence." And Moses, the man of God.' Rabbi Yehoshua ben Yossi said, 'Dividing [the week of] the consecration of Aaron [among the seven days], Moses served as high priest every day of the consecration, as it is said, "Moses and Aaron in their priesthood."'"