The reciter: Muhammad ibn Muqatil narrated to us, Abdullah narrated to us, Yunus narrated to us from al-Zuhri, who said: I heard al-Sa'ib ibn Yazid say:
In the lifetime of Allah's Messenger (ﷺ), and Abu Bakr and `Umar, the Adhan for the Jumua prayer used to be pronounced after the Imam had taken his seat on the pulpit. But when the people increased in number during the caliphate of `Uthman, he introduced a third Adhan (on Friday for the Jumua prayer) and it was pronounced at Az-Zaura' and that new state of affairs remained so in the succeeding years.
إن الأذان يوم الجمعة كان أوله حين يجلس الإمام يوم الجمعة على المنبر في عهد رسول الله صلى الله عليه وسلم وأبي بكر وعمر رضي الله عنهما، فلما كان في خلافة عثمان بن عفان رضي الله عنه وكثروا أمر عثمان يوم الجمعة بالأذان الثالث فأذن به على الزوراء، فثبت الأمر على ذلك Sahih al-Bukhari 916.