Hadith: A man announced (the loss of his camel) in the mosque, saying out loud: Has any one seen the red camel? Upon this the Messenger of Allah (may Allah's peace and blessings be upon him) said: May you not find it! The mosques are only built for the purpose they are built

عن بُريدة رضي الله عنه : أن رجُلاً نَشَدَ في المسجد فقال: من دَعَا إلى الجَمَل الأحمر؟ فقال رسول الله صلى الله عليه وسلم : «لا وجَدْتَ؛ إنما بُنِيَتِ المساجد لما بُنِيَتْ له».
[صحيح] - [رواه مسلم]

Buraydah (may Allah be pleased with him) reported that a man announced (the loss of his camel) in the mosque, saying out loud: "Has any one seen the red camel?" Upon this the Messenger of Allah (may Allah's peace and blessings be upon him) said: "May you not find it! The mosques are built for the purpose they are built."
[Authentic hadith] - [Narrated by Muslim]

Explanation

Buraydah (may Allah be pleased with him) relates in this Hadīth that the Prophet (may Allah's peace and blessings be upon him) heard a man inside the mosque asking if anyone had seen his red camel, and that whoever would find it should let him know. The Prophet supplicated against him that he would not find it, or that Allah would not restore it to him (as in another reporion). He then explained why he supplicated against him, saying that the Houses of Allah were not built for worldly affairs such as asking about lost items or buying and selling; rather, they were built for prayer, the remembrance of Allah, and seeking the Hereafter.