The Messenger of Allah ﷺ prohibited buying and selling in the mosque, announcing aloud about a lost thing, the recitation of a poem in it, and prohibited sitting in a circle (in the mosque) on Friday before the prayer.  

أَنَّ رَسُولَ اللَّهِ ﷺ نَهَى عَنِ الشِّرَاءِ وَالْبَيْعِ فِي الْمَسْجِدِ وَأَنْ تُنْشَدَ فِيهِ ضَالَّةٌ وَأَنْ يُنْشَدَ فِيهِ شِعْرٌ وَنَهَى عَنِ التَّحَلُّقِ قَبْلَ الصَّلاَةِ يَوْمَ الْجُمُعَةِ