Sahih al-Bukhari 916
صحيح البخاري#916Sahihحَدَّثَنَا مُحَمَّدُ بْنُ مُقَاتِلٍ، قَالَ أَخْبَرَنَا عَبْدُ اللَّهِ، قَالَ أَخْبَرَنَا يُونُسُ، عَنِ الزُّهْرِيِّ، قَالَ سَمِعْتُ السَّائِبَ بْنَ يَزِيدَ، يَقُولُ إِنَّ الأَذَانَ يَوْمَ الْجُمُعَةِ كَانَ أَوَّلُهُ حِينَ يَجْلِسُ الإِمَامُ يَوْمَ الْجُمُعَةِ عَلَى الْمِنْبَرِ فِي عَهْدِ رَسُولِ اللَّهِ صلى الله عليه وسلم وَأَبِي بَكْرٍ وَعُمَرَ ـ رضى الله عنهما ـ فَلَمَّا كَانَ فِي خِلاَفَةِ عُثْمَانَ ـ رضى الله عنه ـ وَكَثُرُوا، أَمَرَ عُثْمَانُ يَوْمَ الْجُمُعَةِ بِالأَذَانِ الثَّالِثِ، فَأُذِّنَ بِهِ عَلَى الزَّوْرَاءِ، فَثَبَتَ الأَمْرُ عَلَى ذَلِكَ.
Narrated Az-Zuhri:I heard As-Saib bin Yazid, saying, "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
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
Every narration in Sahih al-Bukhari is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 11:40