From when and which perspective did Imam and Mu'addhin of Masjid start to get paid?

As far I know, in the age of Nabi (sm.), sahabi (ra.), tabeyin (rh.), tabe-tabeyin (rh.), there was no instance of paying Imam and Muajjin (Muadhin/Muezzin) of Masajid. But now-a-days, we see, in almost every Masjid, there remains a paid Imam, a paid Muajjin, a paid Khadim and may be somebody else. From when and which perspective Imam and Muajjin are started to get paid?