2 Samuel 15:12, 31

And while Absalom was offering the sacrifices, he sent for Ahithophel the Gilonite, David’s counselor, from his city Giloh. And the conspiracy grew strong, and the people with Absalom kept increasing.

And it was told David, “Ahithophel is among the conspirators with Absalom.” And David said, “O LORD, please turn the counsel of Ahithophel into foolishness.”