It Is Recommended To Have Two Mu'adhdhin In A Single Masjid

Sahih Muslim · Book 4 · Hadith 380 a

حَدَّثَنَا ابْنُ نُمَيْرٍ، حَدَّثَنَا أَبِي، حَدَّثَنَا عُبَيْدُ اللَّهِ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، قَالَ كَانَ لِرَسُولِ اللَّهِ صلى الله عليه وسلم مُؤَذِّنَانِ بِلاَلٌ وَابْنُ أُمِّ مَكْتُومٍ الأَعْمَى ‏.‏

Ibn Umar reported: The Messenger of Allah (ﷺ) had two Mu'adhdhins, Bilal and 'Abdullah b. Umm Maktum, who (latter) was blind.

Sahih Muslim · Book 4 · Hadith 380 b

وَحَدَّثَنَا ابْنُ نُمَيْرٍ، حَدَّثَنَا أَبِي، حَدَّثَنَا عُبَيْدُ اللَّهِ، حَدَّثَنَا الْقَاسِمُ، عَنْ عَائِشَةَ، مِثْلَهُ ‏.‏

This hadith has been narrated on the authority of 'A'isha by another chain of transmitters.