Hilchos Lashon Hara, chapter 3, section 6

Know, that even if no harm came to that person through saying lashon hara, such as when the listeners did not accept his story, nonetheless, it is considered lashon hara and needs atonement. Furthermore, even if one estimated from the start that no harm would come to the person he spoke of from his story, it is still forbidden to speak derogatorily of him.