Numbers 33:35-39

They journeyed from Abronah and camped at Ezion-geber.

They journeyed from Ezion-geber and camped in the wilderness of Zin, that is, Kadesh.

They journeyed from Kadesh and camped at Mount Hor, at the edge of the land of Edom.

Then Aaron the priest went up to Mount Hor at the command of the Lord, and died there in the fortieth year after the sons of Israel had come from the land of Egypt, on the first day in the fifth month.

Aaron was 123 years old when he died on Mount Hor.