The prohibition of making lost property announcements in the masjid, and what should be said by one who hears a person making such an announcement Sahih Muslim 569 b
Translation
Sulaiman b. Buraida reported on the authority of his father that when the Messenger of Allah (ﷺ) had said prayer a man stood up and said
Who called for a red camel? (Upon this) the Messenger of Allah (ﷺ) said: May it not be restored to you! The mosques are built for what they are meant.