The Sunnah Regarding The Adhan Sunan Ibn Majah 716

Arabic hadith text
حَدَّثَنَا عَمْرُو بْنُ رَافِعٍ، حَدَّثَنَا عَبْدُ اللَّهِ بْنُ الْمُبَارَكِ، عَنْ مَعْمَرٍ، عَنِ الزُّهْرِيِّ، عَنْ سَعِيدِ بْنِ الْمُسَيَّبِ، عَنْ بِلاَلٍ، أَنَّهُ أَتَى النَّبِيَّ ـ صلى الله عليه وسلم ـ يُؤْذِنُهُ بِصَلاَةِ الْفَجْرِ فَقِيلَ هُوَ نَائِمٌ ‏.‏ فَقَالَالصَّلاَةُ خَيْرٌ مِنَ النَّوْمِ الصَّلاَةُ خَيْرٌ مِنَ النَّوْمِ فَأُقِرَّتْ فِي تَأْذِينِ الْفَجْرِ فَثَبَتَ الأَمْرُ عَلَى ذَلِكَ
Translation
It was narrated that Bilal came to the Prophet to call him for the Fajr prayer, and was told

"He is sleeping." He said: "As-salatu khairum minan-nawm, As-salatu khairum minan-nawm (The prayer is better than sleep, the prayer is better than sleep). These words were approved of in the Adhan for the Fajr, and that is how it remained.