I heard the Messenger of Allah (May peace be upon him) as saying; if anyone hears a man crying out in the mosque about something he has lost, he should say: May Allah not restore it to you, for the mosque were not built for this. (Using translation from Abū Dāʾūd 473)   

سَمِعْتُ رَسُولَ اللهِ ﷺ يَقُولُ مَنْ سَمِعَ رَجُلًا يَنْشُدُ فِي الْمَسْجِدِ ضَالَّةً فَلْيَقُلْ لَا أَدَّاهَا اللهُ إِلَيْكَ؛ فَإِنَّ الْمَسَاجِدَ لَمْ تُبْنَ لِهَذَا  

[Machine] The Prophet ﷺ heard an Arab man or a person saying, "Whoever calls to the red camel." The Prophet ﷺ said, "No, you have not found (meaning the mosques were not built) except for what they were built for."  

أَنَّ النَّبِيَّ ﷺ سَمِعَ أَعْرَابِيًّا أَوْ رَجُلًا يَقُولُ مَنْ دَعَا إِلَى الْجَمَلِ الْأَحْمَرِ فَقَالَ النَّبِيُّ ﷺ لَا وَجَدْتَ إِنَّمَا بُنِيَتْ هَذِهِ الْمَسَاجِدُ لِمَا بُنِيَتْ لَهُ