Num 22:13-14
13 The next morning Balaam got up and told Balak's nobles, "Go back home; GOD refuses to give me permission to go with you."
14 So the Moabite nobles left, came back to Balak, and said, "Balaam wouldn't come with us.”

They didn’t say why, just that he wouldn’t come because it was all about what they could see.