When the Mu'adh-dhin pronounced the Adhan for Fajr prayer and the dawn became evident the Prophet ordered a two rakʿat light prayer (Sunna) before the Iqama of the compulsory (congregational) prayer.  

أَنَّ رَسُولَ اللَّهِ ﷺ كَانَ إِذَا اعْتَكَفَ الْمُؤَذِّنُ لِلصُّبْحِ وَبَدَا الصُّبْحُ صَلَّى رَكْعَتَيْنِ خَفِيفَتَيْنِ قَبْلَ أَنْ تُقَامَ الصَّلاَةُ  

Ibn 'Umar reported that Hafsa, the Mother of the Believers, informed him that when the Mu'adhdhin became silent after calling (people) to the dawn prayer, the Messenger of Allah ﷺ commenced the dawn (prayer) when it dawned by observing two short rak'ahs before the commencement of the (Fard) prayer.  

أَنَّ رَسُولَ اللَّهِ ﷺ كَانَ إِذَا سَكَتَ الْمُؤَذِّنُ مِنَ الأَذَانِ لِصَلاَةِ الصُّبْحِ وَبَدَا الصُّبْحُ رَكَعَ رَكْعَتَيْنِ خَفِيفَتَيْنِ قَبْلَ أَنْ تُقَامَ الصَّلاَةُ  

Told him that when the Muaddhin fell silent, Messenger of Allah ﷺ would pray two brief rak'ahs.  

أَنَّ رَسُولَ اللَّهِ ﷺ كَانَ إِذَا سَكَتَ الْمُؤَذِّنُ صَلَّى رَكْعَتَيْنِ خَفِيفَتَيْنِ  

that when the Muaddhin fell silent following the call to Subh prayer and dawn had broken, he would pray two brief rak'ahs before getting up to pray.  

أَنَّ رَسُولَ اللَّهِ ﷺ كَانَ إِذَا سَكَتَ الْمُؤَذِّنُ مِنَ الأَذَانِ لِصَلاَةِ الصُّبْحِ وَبَدَا الصُّبْحُ صَلَّى رَكْعَتَيْنِ خَفِيفَتَيْنِ قَبْلَ أَنْ تُقَامَ الصَّلاَةُ  

It was narrated from Hafsah bint ‘Umar that when the call for the Subh prayer was given, the Messenger of Allah ﷺ would pray two short Rak’ah before going to the prayer.  

أَنَّ رَسُولَ اللَّهِ ﷺ كَانَ إِذَا نُودِيَ لِصَلاَةِ الصُّبْحِ رَكَعَ رَكْعَتَيْنِ خَفِيفَتَيْنِ قَبْلَ أَنْ يَقُومَ إِلَى الصَّلاَةِ  

Yahya related to me from Malik from Nafi from Abdullah ibn Umar that Hafsa, the wife of the Prophet ﷺ told him that the Messenger of Allah ﷺ used to pray two quick rakas when the muadhdhin had finished the adhan for the subh prayer, before the iqama was said for the prayer.  

أَنَّ حَفْصَةَ زَوْجَ النَّبِيِّ ﷺ أَخْبَرَتْهُ أَنَّ رَسُولَ اللَّهِ ﷺ كَانَ إِذَا سَكَتَ الْمُؤَذِّنُ عَنِ الأَذَانِ لِصَلاَةِ الصُّبْحِ صَلَّى رَكْعَتَيْنِ خَفِيفَتَيْنِ قَبْلَ أَنْ تُقَامَ الصَّلاَةُ  

that when the Muaddhin fell silent following the call to Subh prayer and dawn had broken, he would pray two brief rak'ahs before getting up to pray. (Using translation from Nasāʾī 1773)   

أَنَّ رَسُولَ اللهِ ﷺ كَانَ إِذَا سَكَتَ الْمُؤَذِّنُ بِالصُّبْحِ وَبَدَا الصُّبْحُ صَلَّى رَكْعَتَيْنِ خَفِيفَتَيْنِ قَبْلَ أَنْ تُقَامَ الصَّلَاةُ  

that when the Muaddhin fell silent following the call to Subh prayer and dawn had broken, he would pray two brief rak'ahs before getting up to pray. (Using translation from Nasāʾī 1773)   

عَنْ حَفْصَةَ زَوْجِ النَّبِيِّ ﷺ قَالَتْ كَانَ رَسُولُ اللَّهِ ﷺ «إِذَا سَكَتَ الْمُؤَذِّنُ مِنْ أَذَانِ الصُّبْحِ وَبَدَا الصُّبْحُ صَلَّى رَكْعَتَيْنِ خَفِيفَتَيْنِ قَبْلَ أَنْ تُقَامَ الصَّلَاةُ»  

Ibn 'Umar reported that Hafsa, the Mother of the Believers, informed him that when the Mu'adhdhin became silent after calling (people) to the dawn prayer, the Messenger of Allah ﷺ commenced the dawn (prayer) when it dawned by observing two short rak'ahs before the commencement of the (Fard) prayer. (Using translation from Muslim 723a)  

أَنَّ النَّبِيَّ ﷺ كَانَ «إِذَا سَكَتَ الْمُؤَذِّنُ مِنَ الْأَذَانِ لِصَلَاةِ الصُّبْحِ وَبَعْدَ الصُّبْحِ صَلَّى رَكْعَتَيْنِ خَفِيفَتَيْنِ قَبْلَ أَنْ تُقَامَ الصَّلَاةُ»  

Ibn 'Umar reported that Hafsa, the Mother of the Believers, informed him that when the Mu'adhdhin became silent after calling (people) to the dawn prayer, the Messenger of Allah ﷺ commenced the dawn (prayer) when it dawned by observing two short rak'ahs before the commencement of the (Fard) prayer. (Using translation from Muslim 723a)   

رَسُولَ اللهِ ﷺ كَانَ إِذَا سَكَتَ الْمُؤَذِّنُ مِنَ الْآذَانِ لِصَلَاةِ الصُّبْحِ وَبَدَأَ الصُّبْحُ رَكَعَ رَكْعَتَيْنِ خَفِيفَتَيْنِ قَبْلَ أَنْ تُقَامَ الصَّلَاةُ