"The Adhan during the time of Messenger of Allah, Abu Bakr, and Umar was when the Imam came out, [and when] the Iqamah was called for the Salat. Then Uthman [may Allah be pleased with him] added a third call at Az-Zawra."  

كَانَ الأَذَانُ عَلَى عَهْدِ رَسُولِ اللَّهِ ﷺ وَأَبِي بَكْرٍ وَعُمَرَ إِذَا خَرَجَ الإِمَامُ وَإِذَا أُقِيمَتِ الصَّلاَةُ فَلَمَّا كَانَ عُثْمَانُ ؓ زَادَ النِّدَاءَ الثَّالِثَ عَلَى الزَّوْرَاءِ