Assalaamu alaykum. Is it obligatory to appoint a muezzin to call the azan for the masjid given that the messenger of Allaah, sallallahu ‘alayhi wa sallam, appointed Bilaal, may Allah be pleased with him?
All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.
Calling the athaan is a communal obligation (an obligation on the community as a whole) according to the opinion of the Muslim scholars. If a group of Muslims observe this obligation, the liability of the rest of the Muslims in the community is cleared and the obligation is waived from them. It is obligatory to have one person call the athaan in the town if this is enough to inform the people of the prayer times; otherwise, more people should call it.
It is not obligatory to appoint a specific person to call it; rather, whoever is qualified to do so, by being a trustworthy honest Muslim, is allowed to call it, and the rest of the community is exempted from this obligation by his athaan.
However, if the Muslim ruler appointed a specific person to call it, it is impermissible for others to transgress against his right and call it in his presence given the fact that the task of doing so has been assigned to him.
For more benefit, please refer to fatwa 86473.
Allah knows best.
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