Charles Ellicott Commentary 2 Samuel 15:31

"And one told David, saying, Ahithophel is among the conspirators with Absalom. And David said, O Jehovah, I pray thee, turn the counsel of Ahithophel into foolishness." — 2 Samuel 15:31 (ASV)

One told David. —This is no doubt the meaning, but the preposition has dropped out of the Hebrew text, leaving it unintelligible, and reading literally, and David told.