Numbers 33:38

And Aaron the priest went up into Mount Hor, at the
commandment of the Lord
Delivered to Moses:

and died there in the fortieth year after the children of Israel were
come out of Egypt;
not being suffered to go with them into the land of Canaan, because of his sin of unbelief at Kadesh, the last place from whence they came: in Mount Hor he died,

on the first day of the fifth month;
the month Ab, answering to part of July and part of August; so that he lived but four months after his sister Miriam; see ( Numbers 20:1 Numbers 20:25-29 ) .