Rashi on Ki Sisa 33:17

English: גם את הדבר הזה THIS THING ALSO — that My Shechinah shall not rest henceforth upon the other nations of the world, אעשה I WILL DO. And thus He did, for the prophetical words of Balaam (the heathen prophet) were not uttered by reason of the Shechinah resting upon him, but, as Scripture describes it, (Numbers 24:4) “[he saw the vision of the Almighty] fallen, but with eyes uncovered” (i. e. whilst fallen into a sleep his mental eyes were open and he saw in a dream what the Almighty was to reveal unto him) in a state of mind similar to that described by Job (Job 4:12) “a word was by stealth conveyed (יגנב) to me” — they (the heathen prophets) used to hear God’s message through a medium.