Numbers 22:18-20, 35

Balaam answered the servants of Balak, “Even if Balak were to give me his house full of silver and gold, I could not do anything, either small or great, contrary to the command of the LORD my God. Now please, you also stay here tonight, and I will find out what else the LORD will say to me.” God came to Balaam at night and said to him, “If the men have come to call you, get up and go with them, but you shall still do only what I tell you.”

The Angel of the LORD said to Balaam, “Go with the men, but you shall speak only what I tell you.” So Balaam went along with the leaders of Balak.