The phrase "a narrator stating" is correct and usable in written English.
It can be used when discussing the actions or role of a narrator in a story or narrative context.
Example: "In the novel, a narrator stating the protagonist's thoughts adds depth to the character's development."
Alternatives: "a narrator expressing" or "a narrator declaring".
When he is about to reveal the identity of Cartman's father, a narrator states that the answer will be revealed in the new South Park episode five weeks later, much to Cartman's annoyance.
A narrator states that "she took home $46 million and now she's talking about lowering the minimum wage," while an image of a local newspaper article with the headline "McMahon: Congress Should Consider Lowering Minimum Wage" shows up on screen.
The show opens with the narrator stating "It was a typical week for us Jewish 20 something's living with our parents on Long Island".
At one point in the narration, the narrator states a kind of "article of faith" that ratifies these places' right to exist: these places are, in and of themselves, perfect; nothing humans can do can add to what is here; anything we add can only mar this place.
The narrator states that they once overheard a "high-minded", "golden-haired", and "white-armed" maiden speaking with a "glossy-beaked raven".
The narrator states that its origin appears to rely on an "ancient" prophecy: "A lofty name shall have a fearful fall when, as the rider over his horse, the mortality of Metzengerstein shall triumph over the immortality of Berlifitzing".
The narrator states that it is right for a father to support his child in his infancy, but questions whether the father should continue to hold the child's hand even after he is grown up.
The narrator states at Persuasion's end that "the dread of a future war [was] all that could dim her sunshine".
Finally, the narrator stated that the decision aid would anonymously collect responses into a printable Personal Decision Summary that they could discuss with their family and doctor(s).
The narrator states he is going to quit.
