Bilal made a call to prayer before the break of dawn; the Prophet ﷺ, therefore, commanded him to return and make a call: Lo! the servant of Allah (i.e. I) had slept (hence this mistake). The version of Musa has the addition: He returned and made a call: Lo! the servant of Allah had slept. Abu Dawud said: This tradition has been narrated by al-Darawardi from 'Ubaid Allah on the authority of Ibn 'Umar saying: There was a mu'adhdhin of 'Umar, named Mas'ud. He then narrated the rest of the tradition. This version is more correct than that one.  

أَنَّ بِلاَلاً أَذَّنَ قَبْلَ طُلُوعِ الْفَجْرِ فَأَمَرَهُ النَّبِيُّ ﷺ أَنْ يَرْجِعَ فَيُنَادِيَ أَلاَ إِنَّ الْعَبْدَ قَدْ نَامَ أَلاَ إِنَّ الْعَبْدَ قَدْ نَامَ زَادَ مُوسَى فَرَجَعَ فَنَادَى أَلاَ إِنَّ الْعَبْدَ نَامَ