´It was narrated from Abu 'Abdullah, the freed slave of Shaddad bin Had that:` He heard Abu Hurairah say: "I heard the Messenger of Allah say: 'Whoever hears a man making a lost-and-found announcement in the mosque, let him say: "May Allah not return it to you!" For the mosques were not built for that.'"
Hadith Referenceسنن ابن ماجه / كتاب المساجد والجماعات / 767
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:صحيح مسلم