The Messenger of Allah ﷺ had two muezzins, Bilal and Ibn Umm Maktum.
كان لرسول الله ﷺ مؤذنان، بلال وابن أم مكتوم.
Muslim narrated it in the Book of Prayer (380), from Ibn Numayr, from his father, from Ubaydullah, from Qasim, from Ayesha, and he mentioned it, though Muslim did not give its wording but instead referred it to the hadith of Ibn Umar.Ibn Abu Shayba narrated it from her, and she said, "The Messenger of Allah ﷺ had three muezzins, Bilal, Abu Mahzura, and Ibn Umm Maktum." He narrated it from Yahya bin Adam, from Israil, from Abu Ishaq, from Aswad, from Ayesha. Ibn Khuzayma also narrated it through him and said, "The report is sahih. Whoever said he had two muezzins meant the two who called the adhan in Madinah, and whoever said he had three meant Abu Mahzura, who called the adhan in Makkah." See Ithaf Mahra (2/126).I say, likewise Saad bin Aaidh, or Ibn Abdul-Rahman, the freed slave of the Ansari known as Saad Qaraz, was the muezzin of the Messenger of Allah ﷺ in Quba, as recorded by Hakim (3/608) through the route of Baqiyya, from Zubaydi, from Zuhri, from Hafs bin Umar bin Saad Qaraz, that his father and his uncles informed him that Saad Qaraz was a muezzin for the people of Quba, and Umar bin Khattab relocated him and took him on as a muezzin for the masjid of the Messenger of Allah ﷺ. Hakim and Dhahabi passed over it in silence, and in the chain is Hafs bin Umar bin Saad, whom Ibn Hajar ranked as "acceptable." This was after the Messenger of Allah ﷺ died, and Bilal left off giving the adhan and moved to Syria.He is called Saad Qaraz because he used to trade in qaraz. Baghawi narrated from Qasim bin Hasan bin Muhammad bin Amr bin Hafs bin Amr bin Saad Qaraz, from his forefathers, that Saad complained to the Prophet ﷺ of having little means, so the Prophet ﷺ instructed him to engage in trade. He went out to the market and bought some qaraz, sold it, and made a profit on it. He mentioned this to the Prophet ﷺ, who told him to keep doing that. Ibn Hajar mentioned this in Al-Isabah (2/29).Ibn Abdul-Barr said in Al-Istiab, "He continued giving the adhan in the masjid of the Messenger of Allah ﷺ until he died, and his sons inherited the giving of the adhan there after him, down to the time of Malik and beyond as well."