Mukhtasar Bukhari

Sayyiduna Sa’ib bin Yazid (may Allah be pleased with him) says that on the day of Jumu’ah, the adhan during the time of the Prophet (peace and blessings of Allah be upon him), and during the era of the Commander of the Faithful Abu Bakr as-Siddiq and ‘Umar al-Faruq (may Allah be pleased with them both), used to be given when the Imam sat on the pulpit. Then ‘Uthman (may Allah be pleased with him) became the Caliph and (the number of) Muslims increased, so ‘Uthman (may Allah be pleased with him) added a third adhan at Zawra. (Imam Bukhari, may Allah have mercy on him, said that Zawra is the name of a place in the market of Madinah.)