Yahya related to me from Malik from Ibn Shihab that Thalaba ibnAbi Malik al Quradhi informed him that in the time of Umar ibn alKhattab they used to pray on the day of jumua until Umar came out, andwhen Umar came out and sat on the mimbar and the muadhdhins called theadhan, they would sit and talk, and then when the muadhdhins weresilent and Umar stood to give the khutba, they would pay attention andno-one would speak .Ibn Shihab said, "The imam coming outstops prayer and his speaking stops conversation."
USC-MSA web (English) reference: Book 5, Hadith 7
Arabic reference: Book 5, Hadith 232