Riyad as-Salihin 17:186

Abu Hurairah (May Allah be pleased with him) said:

The Messenger of Allah (ﷺ) said, "If anyone hears a man inquiring in the mosque about something he has lost, he should say: 'La raddaha Allahu 'alaika (May Allah not restore it to you),' for mosques are not built for this purpose." [Muslim]