2 Samuel 15:6-10
English Standard Version
7And at the end of four years Absalom said to the king, "Please let me go and pay my vow, which I have vowed to the Lord, in Hebron.
8For your servant vowed a vow while I lived at Geshur in Aram, saying, ‘If the Lord will indeed bring me back to Jerusalem, then I will offer worship to the Lord.’"
9The king said to him, "Go in peace." So he arose and went to Hebron.
10But Absalom sent secret messengers throughout all the tribes of Israel, saying, "As soon as you hear the sound of the trumpet, then say, ‘Absalom is king at Hebron!’"