John Gill 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)

And one of his servants said, none, my lord, O king

He believed everyone of his counsellors were true and faithful to him:

but Elisha the prophet, that is in Israel, tells the king of Israel the words that you speak in your bedchamber ;

what is said in the most private place, and in the most secret manner:

this man had heard much of Elisha, by Naaman, very probably; or perhaps he had attended him in his journey to Israel for a cure, and so might have personal knowledge of Elisha, and be acquainted with the affair of Gehazi; from where he concluded, that he, who had the thoughts of men revealed to him, had knowledge of their words and counsels, though ever so secret; see (Ecclesiastes 10:20) .