Rashi on Numbers 22:18/רש"י על במדבר כ״ב:י״ח

1מלא ביתו כסף וזהב [IF BALAK WOULD GIVE ME HIS HOUSE] FULL OF SILVER AND GOLD — This tells us that he was avaricious and covetous of other peoples wealth. He said: He ought to give me all his silver and gold, for, behold, he would otherwise have to hire many armies to fight against them. Even then it is doubtful whether he would conquer or not conquer, but “I” would certainly conquer (Midrash Tanchuma, Balak 6).

2לא אוכל לעבר I CANNOT GO BEYOND [THE WORD OF THE LORD] — Against his own will he divulged to them that he was under the control of others, and he prophesied here that he would be unable to annul those blessings with which the patriarchs had been blessed by the mouth of God (Midrash Tanchuma, Balak 6).