I attend a shul where there is a small minyan, often only ten people. It is very important to me that all ten should be davening in order to have tefilla btzibbur (MB 90:28). One of the people there was specifically asked by the gabbai not to daven elsewhere before coming. However, he didn’t listen and davened elsewhere before coming, which he admitted to me. May I tell the gabbai this and ask him to go find someone else for the minyan (which he will do since he knows it is important to me), or is it lashon hara against this person since the gabbai will be upset with him for not listening?
Thank you for your question.
You are allowed to tell this to the gabbai, because it is l’toeles, not merely to the gabbai but to everyone else who is davening in the minyan. I am assuming that the person knows that he is causing the minyan to be one of hashlomo, and not a full minyan.