Mishkat al-Masabih 645
He also said:
When I asked God’s Messenger to teach me the sunna relating to the adhan he wiped the forepart of his head and said: You must say, “God is most great. God is most great. God is most great. God is most great,” raising your voice while saying these words. Then you must say, “I testify that there is no god but God. I testify that there is no god but God. I testify that Muhammad is God’s Messenger. I testify that Muhammad is God’s Messenger,” lowering your voice while saying these words. Then you must raise your voice in making the testimony, “I testify that there is no god but God. I testify that there is no god but God. I testify that Muhammad is God’s Messenger. I testify that Muhammad is God’s Messenger. Come to prayer. Come to prayer. Come to salvation. Come to salvation”; and if it is the Morning Prayer you must say, “Prayer is better than sleep. Prayer is better than sleep. God’s is most great. God is most great. There is no god but God.” 

Abu Dawud transmitted it.
وَعَنْهُ قَالَ: قُلْتُ يَا رَسُولَ اللَّهِ عَلِّمْنِي سنة الْأَذَان قَالَ: فَمسح مقدم رَأسه. وَقَالَ: 
" وَتقول اللَّهُ أَكْبَرُ اللَّهُ أَكْبَرُ اللَّهُ أَكْبَرُ اللَّهُ أَكْبَرُ تَرْفَعُ بِهَا صَوْتَكَ ثُمَّ تَقُولَ: أَشْهَدُ أَن لَا إِلَه إِلَّا الله أشهد أَن لَا إِلَهَ إِلَّا اللَّهُ أَشْهَدُ أَنَّ مُحَمَّدًا رَسُولُ اللَّهِ أَشْهَدُ أَنَّ مُحَمَّدًا رَسُولُ اللَّهِ تَخْفِضُ بِهَا صَوْتَكَ ثُمَّ تَرْفَعُ صَوْتَكَ بِالشَّهَادَةِ: أَشْهَدُ أَنْ لَا إِلَهَ إِلَّا اللَّهُ أَشْهَدُ أَن لَا إِلَه إِلَّا الله أشهد أَن مُحَمَّدًا رَسُولُ اللَّهِ أَشْهَدُ أَنَّ مُحَمَّدًا رَسُولُ اللَّهِ حَيَّ عَلَى الصَّلَاةِ حَيَّ عَلَى الصَّلَاةِ حَيَّ عَلَى الْفَلَاحِ حَيَّ عَلَى الْفَلَاحِ فَإِنْ كَانَ صَلَاةُ الصُّبْحِ قُلْتَ: الصَّلَاةُ خَيْرٌ مِنَ النَّوْمِ الصَّلَاةُ خَيْرٌ مِنَ النَّوْمِ اللَّهُ أَكْبَرُ اللَّهُ أَكْبَرُ لَا إِلَهَ إِلَّا اللَّهُ " رَوَاهُ أَبُو دَاوُد