Albert Barnes Commentary 2 Samuel 9:11

"Then said Ziba unto the king, According to all that my lord the king commandeth his servant, so shall thy servant do. As for Mephibosheth, [said the king], he shall eat at my table, as one of the king`s sons." — 2 Samuel 9:11 (ASV)

Said the king - There is nothing in the Hebrew to warrant the insertion of these words. The words are: So Mephibosheth ate at my table as one of the king’s sons. From this, it follows that the narrator is David himself.