Absalom said to Ahithophel, "Give us your advice. What should we do?"
Ahithophel answered, "Lie with your father's concubines whom he left to take care of the palace. Then all Israel will hear that you have made yourself a stench in your father's nostrils, and the hands of everyone with you will be strengthened."
So they pitched a tent for Absalom on the roof, and he lay with his father's concubines in the sight of all Israel.1
References for 2 Samuel 16:22
Now in those days the advice2 Ahithophel gave was like that of one who inquires of God. That was how both David3 and Absalom regarded all of Ahithophel's advice.
References for 2 Samuel 16:23