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 ofthe Prophet (ﷺ) there was only one Mu'adh-dhin and the Adhan used to be pronounced only after theImam had taken his seat (i.e. on the pulpit).