2 Samuel 16:20-23
16:20 Then Absalom said to Ahithophel, “Give us your advice. What should we do?”
16:21 Ahithophel replied to Absalom, “Have sex with your father’s concubines whom he left to care for the palace. All Israel will hear that you have made yourself repulsive to your father. Then your followers will be motivated to support you.”
16:22 So they pitched a tent for Absalom on the roof, and Absalom had sex with his father’s concubines in the sight of all Israel.
16:23 In those days Ahithophel’s advice was considered as valuable as a prophetic revelation. Both David and Absalom highly regarded the advice of Ahithophel.