Rashi on Numbers 22:23/רש"י על במדבר כ״ב:כ״ג

1ותרא האתון AND THE SHE-ASS SAW [THE ANGEL] — but he did not see him, for the Holy One, blessed be He, gave an animal power to see more than the man, for just because he possesses sense his mind would become perturbed if he sees noxious beings.

2וחרבו שלופה בידו AND HIS SWORD DRAWN IN HIS HAND — He (God) said: This wicked man has abandoned the tools of his own craft, — for the offensive weapons of the heathen peoples consist in the sword, — and he is attacking them with his mouth which is their metier; I will take his implement and come against him with his own metier. Thus, indeed, was his end (Numbers 31:8): “And Balaam the son of Beor they slew by the sword” (Midrash Tanchuma 4:7:23).