Rashi on Numbers 22:20/רש"י על במדבר כ״ב:כ׳

1אם לקרא לך IF [THE MEN COME] TO CALL THEE — If the call be for you, for your benefit, and you think to take a fee for it.

2קום לך אתם ARISE, GO WITH THEM, ואך BUT, in spite of yourself, את הדבר אשר אדבר אליך אתו תעשה THE WORD WHICH I SHALL SPEAK TO THEE, THAT SHALL YOU DO, and, nevertheless, Balaam went (as it is stated in the next verse), for he said: perhaps I may persuade Him and He will agree that I should curse.