Numbers 33:37-39

Young's Literal Translation

³⁷ And they journey from Kadesh, and encamp in mount Hor, in the extremity of the land of Edom.

³⁸ And Aaron the priest goeth up unto mount Hor, by the command of Jehovah, and dieth there, in the fortieth year of the going out of the sons of Israel from the land of Egypt, in the fifth month, on the first of the month;

³⁹ and Aaron [is] a son of a hundred and twenty and three years in his dying in mount Hor.