Rashi on Numbers 20:23/רש"י על במדבר כ׳:כ״ג

1על גבול ארץ אדום BY THE BOUNDARY OF THE LAND OF EDOM — This (the statement that Aaron died here) tells us that because they here wished to join themselves in close friendship with the wicked, a breach was made in their works and they had to lose this righteous man, Aaron. Similarly does the prophet say, (II Chronicles 20:37) “Because thou hast joined thyself with Ahaziah, the Lord hath made a breach in thy works” (Midrash Tanchuma, Chukat 14).