Parashas Eikev · Passuk 10:6
From Beeroth-bene-jaakanaBeeroth-bene-jaakan Lit. “wells of Bene-jaakan”; cf. Num. 33.31–32. the Israelites marched to Moserah. Aharon died there and was buried there; and his son Eleazar became priest in his stead.
Torah Temimah points to Yerushalmi Yoma 1:1.
TT lemma: מוסרה שם מת אהרן, וכי במוסרה מת והלא בהר ההר מת (פ' מסעי), אלא מכיון ש (unit 1 of 2).
English: “At Moserah Aharon died” — but did he die at Moserah? He died at Hor HaHar. Rather, when he died the clouds of glory departed, the Canaanites sought to attack Israel, and Israel sought to return to Egypt and traveled backward eight stages, corresponding to the stations listed in Masei. The tribe of Levi pursued them and blood was shed; they recognized that the cause was their failure to perform kindness with that righteous man, so they eulogized him and performed kindness, and Scripture counts it as though he died and was buried there.
Custom (Yerushalmi — Moserah as site of mourning for Aharon)
The Torah places Aharon’s death at Moserah because of the national crisis and the eulogy that followed the reverse march.