2 Samuel 15:7-12

7And it came to pass after forty years, that Absalom said unto the king, I pray thee, let me go and pay my vow, which I have vowed unto the Lord, in Hebron. 8For thy servant vowed a vow while I abode at Geshur in Syria, saying, If the Lord shall bring me again indeed to Jerusalem, then I will serve the Lord. 9And the king said unto him, Go in peace. So he arose, and went to Hebron.

10But Absalom sent spies throughout all the tribes of Israel, saying, As soon as ye hear the sound of the trumpet, then ye shall say, Absalom reigneth in Hebron. 11And with Absalom went two hundred men out of Jerusalem, that were called; and they went in their simplicity, and they knew not any thing. 12And Absalom sent for Ahithophel the Gilonite, David’s counsellor, from his city, even from Giloh, while he offered sacrifices. And the conspiracy was strong; for the people increased continually with Absalom.