Abu Dawud

1090. Commentary:
The background of this narration is that after the best generations (khayr al-quroon), when mosques began to be built larger and populations increased, a separate muezzin (mu’adhdhin) started to be appointed at each minaret of the congregational mosques (jami‘ masajid), so for one prayer, several muezzins would give the call to prayer (adhan) in a single mosque. The purpose of the hadith is that it is the Sunnah for only one muezzin to give the adhan, not for several to do so. In the era of the Messenger (sallallahu alayhi wa sallam), besides Bilal (radi Allahu anhu), Ibn Umm Maktum, Sa‘d al-Qaraz, and Abu Mahdhurah (radi Allahu anhum ajma‘in) were also muezzins. Abu Mahdhurah (radi Allahu anhu) was in Makkah, and Sa‘d (radi Allahu anhu) was in Quba’.