Musar do Liczb 21:28

They also expounded "the city of Sichon" in a different fashion, viz. (Ibid. 28): "For a fire has gone forth from Cheshbon, a flame from the city of Sichon. It has consumed Ar of Moav, the possessors of Arnon" — If a man makes himself like a young ass [ayir - similar to ir, "city"], which docilely follows the cajoling talk [(sicha, intimated by "Sichon") of its driver], in this case, the yetzer, "A fire will go forth from Cheshbon" — from those who reckon the account of the world, "a flame from the city of Sichon" — the tzaddikim, who are referred to as "sprouts" [sichin, intimated by "Sichon"], and it shall consume those who make no reckoning of their end." The explanation (in my humble opinion) is, according to the other phenomenon of which Chazal apprise us, that the rasha takes his portion and the portion of his neighbor [the tzaddik] in Gehinnom. This is the intent of "for a fire has gone forth from Cheshbon" — that is, the fire of Gehinnom, created by the sins of the tzaddikim will go forth from them, i.e., it will not prevail over them. And over whom will it prevail? Over the reshaim, who make no reckoning of their end. And thus, the conclusion of the verse: "It has consumed Ar of Moav" — intimating that it will consume the lusters, (viz. [Ibid. 25:1): "And the people began to lust after the daughters of Moav"). (Ibid. 21:28): 'the possessors of the heights of Arnon' — the haughty of spirit."