Rashi on Numbers 23:28/רש"י על במדבר כ״ג:כ״ח

1ראש הפעור THE TOP OF PEOR — Balak was a great soothsayer and he foresaw that they would once be punished on account of Peor, but he knew not by what. He said: Perhaps the curse will fall upon them from there (be effective against them if pronounced there). So, too, all astrologers: they see something that will once happen but they know not exactly what they see (cf. Sotah 12b).