Sahih Muslim , Book 4, Hadith 7 (In-Book) ⓘ
Ibn Umar reported: The Messenger of Allah had two Mu'adhdhins, Bilal and 'Abdullah b. Umm Maktum, who (latter) was blind.
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 .
also referenced under: Hadith 380 (Reference) & Book 4, Hadith 741 (USC-MSA)