The Sunnah Regarding The Adhan
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 . فَقَالَ الصَّلاَةُ خَيْرٌ مِنَ النَّوْمِ الصَّلاَةُ خَيْرٌ مِنَ النَّوْمِ فَأُقِرَّتْ فِي تَأْذِينِ الْفَجْرِ فَثَبَتَ الأَمْرُ عَلَى ذَلِكَ .
It was narrated that Bilal came to the Prophet (ﷺ) 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.