Sunan an-Nasa'i 646

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 (S.A.W) said:"Allah and His angels say salah upon the front 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

Reference

Sunan an-Nasa'i 646

In-book

Book 7, Hadith 21