Albert Barnes Commentary 2 Kings 6:12

"And one of his servants said, Nay, my lord, O king; but Elisha, the prophet that is in Israel, telleth the king of Israel the words that thou speakest in thy bedchamber." — 2 Kings 6:12 (ASV)

In your bedchamber - literally, "in the secret place of your bedchamber," that is, in the greatest possible secrecy. The seclusion of the harem must be taken into account for the full appreciation of the force of the phrase. Probably the Syrian lord who answered Benhadad had received his intelligence from some of the Israelites.