2 Samuel 15:9-10

9“All right,” the king told him. “Go and fulfill your vow.” So Absalom went to Hebron.

10But while he was there, he sent secret messengers to all the tribes of Israel to stir up a rebellion against the king. “As soon as you hear the ram’s horn,” his message read, “you are to say, ‘Absalom has been crowned king in Hebron.’”