Prayer (Kitab Al-Salat): Details of Commencing Prayer
Dawud :: Book 3 : Hadith 1074
Narrated Abdullah ibn Amr ibn al-'As:
The Apostle of Allah (peace_be_upon_him) 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.