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Ibn ‘Umar reported God’s Messenger as saying, “If anyone calls the adhan for twelve years, paradise is guaranteed to him; sixty blessings will be recorded for him for every day’s calling of the adhan and thirty blessings for every iqama.” Ibn Majah transmitted it.
Source: sunnah.com
Other translations
Arabic
وَعَنِ ابْنِ عُمَرَ أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: «مَنْ أَذَّنَ ثِنْتَيْ عَشْرَةَ سَنَةً وَجَبَتْ لَهُ الْجَنَّةُ وَكُتِبَ لَهُ بِتَأْذِينِهِ فِي كُلِّ يَوْمٍ سِتُّونَ حَسَنَةً وَلِكُلِّ إِقَامَة ثَلَاثُونَ حَسَنَة» . رَوَاهُ ابْن مَاجَه
sunnah.com