At the LORD’s command, Aaron the priest climbed Mount Hor and died there on the first day of the fifth month, in the fortieth year after the Israelites had come out of the land of Egypt.
Jewish Publication Society of America Version (JPS1917) - Numbers 33:38 >And Aaron the priest went up into mount Hor at the commandment of the LORD, and died there, in the fortieth year after the children of Israel were come out of the land of Egypt, in the fifth month, on the first day of the month.