2 Samuel 16:23

Now in those days the advice of Ahithophel was like the consultation of the word of God. Such was the regard that both David and Absalom had for Ahithophel’s advice.

And the counsel of Ahithophel, which he counselled in those days, was as if a man had enquired at the oracle of God: so was all the counsel of Ahithophel both with David and with Absalom.