2 Samuel 16:20-23

Then Absalom spoke to Ahithophel, “Are you ready to give counsel? What do we do next?” Ahithophel told Absalom, “Go and sleep with your father’s concubines, the ones he left to tend to the palace. Everyone will hear that you have openly disgraced your father, and the morale of everyone on your side will be strengthened.” So Absalom pitched a tent up on the roof in public view, and went in and slept with his father’s concubines. The counsel that Ahithophel gave in those days was treated as if God himself had spoken. That was the reputation of Ahithophel’s counsel to David; it was the same with Absalom.