Mishkat al-Masabih 4 Prayer كتاب الصلاة 85

وَعَنْ عَبْدِ الرَّحْمَنِ بْنِ سَعْدِ بْنِ عَمَّارِ بْنِ سَعْدٍ مُؤَذِّنِ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: حَدَّثَنِي أَبِي عَنْ أَبِيهِ عَنْ جَدِّهِ أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ أَمَرَ بِلَالًا أَنْ يَجْعَلَ أُصْبُعَيْهِ فِي أُذُنَيْهِ وَقَالَ: «إِنَّه أرفع لصوتك» . رَوَاهُ ابْن مَاجَه

‘Abd ar-Rahman b Sa’d b. ‘Ammar b. Sa‘d, the mu’adhdhin * of God’s Messenger, said that his father told him from his father from his grandfather that God’s Messenger commanded Bilal to put his fingers in his ears, saying that it made the voice louder. * The mu’adhdhin here mentioned was Sa‘d, great-grandfather of ‘Abd ar-Rahman. Ibn Majah transmitted it.