Charles Ellicott Commentary Numbers 24:10

"And Balak`s anger was kindled against Balaam, and he smote his hands together; and Balak said unto Balaam, I called thee to curse mine enemies, and, behold, thou hast altogether blessed them these three times." — Numbers 24:10 (ASV)

And he smote his hands together. —Striking the hands was a sign of strong feeling, whether of scorn, indignation, or despair. (Lamentations 2:15).