When did paid professional priest( imam , ulema etc.) become a thing in Islam?

I think during early periods of Islam (Rashidun caliphate) they didn't exist. Imam were just community leaders or commander of army who also leads prayers, ulema's equivalents was basically respected elders or just learned people of society. They probably didn't considered it to be their profession (means of living or earning money). Sort of like hobbyist fisher-man would not state fishing as their profession or job. During early period everyone was more or less equal in terms of religious understanding and duty (everyone understood the Quran properly and if they were lacking in something they would discuss it with others **as student discuss among themselves**). But today there is basically two class of people : priestly class and general population. This priestly class are supposed to be more learned, more practicing and strict. And they specialize in it like doctor or engineer. They have certificates and they get paid. General people ask them about religious affair **as students ask their teacher.** So how and when did this division happen ? ___ https://islam.stackexchange.com/questions/30956/from-when-and-which-perspective-did-imam-and-muaddhin-of-masjid-start-to-get-pa this might be a duplicate or maybe not not asking if halal or haram, or how is it today rather I am interested in it's origin. In particular, I personaly think Ummayad Caliphate might have something to do with it. Rashidun Caliphate was democratic in nature. Ummayad was authoratarian whose source of power was military might rather will of people. Ummayads were not very religious, but still need to pretend to be religious for controlling populace. So Ummayads needed to control the narrative, control interpretation of islam in ways that would suit them. Which means they need to **control licence of who have the authority to interpret islam.** And bar common people from having any say. Else people might see that they are doing unislamic things and rebel against them. someone who is familliar with history of Ummayad, Abbasid might have an answer. So anyone have any idea about this?