2 Samuel 16:21-25

Ahithophel said to Absalom, “Have relations with your father’s concubines, whom he has left behind to take care of the house; then all Israel will hear that you have made yourself repulsive to your father. The hands of all who are with you will also be strengthened.”

So they pitched a tent for Absalom on the roof, and Absalom had relations with his father’s concubines in the sight of all Israel.

Now the advice of Ahithophel, which he gave in those days, was taken as though one inquired of the word of God; so was all the advice of Ahithophel regarded by both David and Absalom.