Rashi on Numbers 22:30/רש"י על במדבר כ״ב:ל׳

1ההסכן הסכנתי — Understand this as the Targum does — HAVE I EVER LEARNT? Similar is, (Job 22:2) “Does a man learn (יסכן) for God’s benefit” (see Rashi on this verse). And our Rabbis have explained this verse in the Talmud: They said to him, “What is the reason you are not riding on a horse?” He replied to them: “I have left it in the meadow grass” (i.e., I have put it out to graze). Whereupon the ass exclaimed: Am I not your ass upon whom thou hast ridden from my very youth unto this day?!” (so you see, you have never possessed a horse) — as it is related in Treatise Avodah Zarah 4b.