The first adhan used to be when the imam sat on the minbar on Friday, at the time of the Messenger of Allah (ﷺ) and Abu Bakr and 'Umar. During the caliphate of 'Uthman, when the number of people increased, 'Uthman commanded that a third adhan be given on Friday, so that adhan was given from the top of Az-Zawra, and that is how it remained.