Al-Sa'ib b. Yazid said: During the time of the Prophet (ﷺ) and Abu Bakr and 'Umar the call to the Friday prayer was first made at the time when the imam was seated on the pulpit (for giving the sermon). When the time of 'Uthman came, and the people became abundant, 'Uthman ordered to make a third call to the Friday prayer. It was made on al-Zaura' (a house in Medina). The rule of action continued to the same effect.
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا مُحَمَّدُ بْنُ سَلَمَةَ الْمُرَادِيُّ، حَدَّثَنَا ابْنُ وَهْبٍ، عَنْ يُونُسَ، عَنِ ابْنِ شِهَابٍ، أَخْبَرَنِي السَّائِبُ بْنُ يَزِيدَ، أَنَّ الأَذَانَ، كَانَ أَوَّلُهُ حِينَ يَجْلِسُ الإِمَامُ عَلَى الْمِنْبَرِ يَوْمَ الْجُمُعَةِ فِي عَهْدِ النَّبِيِّ صلى الله عليه وسلم وَأَبِي بَكْرٍ وَعُمَرَ - رضى الله عنهما - فَلَمَّا كَانَ خِلاَفَةُ عُثْمَانَ وَكَثُرَ النَّاسُ أَمَرَ عُثْمَانُ يَوْمَ الْجُمُعَةِ بِالأَذَانِ الثَّالِثِ فَأُذِّنَ بِهِ عَلَى الزَّوْرَاءِ فَثَبَتَ الأَمْرُ عَلَى ذَلِكَ .
sunnah.com