Numbers 33:39 Midrash

וְאַהֲרֹ֔ן בֶּן־שָׁלֹ֧שׁ וְעֶשְׂרִ֛ים וּמְאַ֖ת שָׁנָ֑ה בְּמֹת֖וֹ בְּהֹ֥ר הָהָֽר׃ (ס)

And Aaron was a hundred and twenty and three years old when he died in mount Hor.

Read midrashic interpretation of Numbers 33:39: and classical rabbinic exegesis.