أَخْبَرَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، قَالَ حَدَّثَنَا مُعَاذُ بْنُ هِشَامٍ، قَالَ حَدَّثَنِي أَبِي، عَنْ قَتَادَةَ، عَنْ أَبِي إِسْحَاقَ الْكُوفِيِّ، عَنِ الْبَرَاءِ بْنِ عَازِبٍ، أَنَّ نَبِيَّ اللَّهِ صلى الله عليه وسلم قَالَ ‏"‏ إِنَّ اللَّهَ وَمَلاَئِكَتَهُ يُصَلُّونَ عَلَى الصَّفِّ الْمُقَدَّمِ وَالْمُؤَذِّنُ يُغْفَرُ لَهُ بِمَدِّ صَوْتِهِ وَيُصَدِّقُهُ مَنْ سَمِعَهُ مِنْ رَطْبٍ وَيَابِسٍ وَلَهُ مِثْلُ أَجْرِ مَنْ صَلَّى مَعَهُ ‏"‏ ‏.‏

It was narrated from Al-Bara bin 'Azib that the Prophet of Allah (PBUH) said: "Allah and His angels say salah upon the from rows, and the Mu'adhdhin will be forgiven as far as his voice reaches, and whatever hears him, wet or dry, will confirm what he says, and he will have a reward like that of those who pray with him." Translation Not Available

Book reference: Sunan An Nisai Book 7 Hadith 653
Web reference: Sunan An Nisai Volume 1 Book 7 Hadith 647