Mishkat al-Masabih 665
‘Uqba b. ‘Amir reported God’s Messenger as saying:
God is pleased with a shepherd on the top of a rock on a mountain who makes the call to prayer and prays. God says, “Look at this servant of Mine who makes the call to prayer, observes the prayer and fears Me. I forgive My servant and will cause him to enter paradise.” 

Abu Dawud and Nasa’i transmitted it.
وَعَنْ عُقْبَةَ بْنِ عَامِرٍ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «يَعْجَبُ رَبُّكَ مِنْ رَاعِي غَنَمٍ فِي رَأْسِ شَظِيَّةٍ لِلْجَبَلِ يُؤَذِّنُ بِالصَّلَاةِ وَيُصَلِّي فَيَقُولُ اللَّهُ عَزَّ وَجَلَّ انْظُرُوا إِلَى عَبْدِي هَذَا يُؤَذِّنُ وَيُقِيمُ الصَّلَاةَ يَخَافُ مِنِّي قَدْ غَفَرْتُ لِعَبْدِي وَأَدْخَلْتُهُ الْجَنَّةَ» . رَوَاهُ أَبُو دَاوُد وَالنَّسَائِيّ