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The person who increased the number of Adhans for the Jumua prayers to three was `Uthman bin `Affan and it was when the number of the (Muslim) people of Medina had increased. In the lifetime of the Prophet (ﷺ) there was only one Mu'adh-dhin

`Uthman bin `Affan introduced the second Adhan on Fridays when the number of the people in the mosque increased. Previously the Adhan on Fridays used to be pronounced only after the Imam had taken his seat (on the pulpit).

There was no other mu'adhdhin of the Messenger of Allah (ﷺ). He then narrated the tradition which is incomplete.

"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."