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  

A mu'adhdhin of ‘Umar, named Masruh, called the Adhan for the morning prayer before the break of dawn; ‘Umar commanded him (to repeat). The narrator reported the tradition in a similar way. Abu Dawud said: This tradition has been transmitted 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 one.  

يُقَالُ لَهُ مَسْرُوحٌ أَذَّنَ قَبْلَ الصُّبْحِ فَأَمَرَهُ عُمَرُ فَذَكَرَ نَحْوَهُ  

The Messenger of Allah ﷺ said to Bilal: Do not call adhan until the dawn appears clearly to you in this way, stretching his hand in latitude. Abu Dawud said: Shaddad did not see Bilal.  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ لَهُ لاَ تُؤَذِّنْ حَتَّى يَسْتَبِينَ لَكَ الْفَجْرُ هَكَذَا وَمَدَّ يَدَيْهِ عَرْضًا