As-Sa'ib bin Yazid said:
"The third adhan was ordered by 'Uthman when the number of people in Al-Madinah increased. The Messenger of Allah (ﷺ) only had one adhan, and the adhan on Friday was when the imam sat down." (ES)
App reference (ES): Book 14, Hadith 30 (ES)
English reference (ES): Vol. 2, Book 14, Hadith 1394 (ES)
Arabic reference (ES): Book 14, Hadith 1404 (ES)