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  

It was narrated from Ibn ‘Umar that when the dawn illuminated, the Prophet ﷺ would pray two Rak’ah. (Using translation from Ibn Mājah 1143)   

أَنَّ النَّبِيَّ ﷺ كَانَ إِذَا طَلَعَ الْفَجْرُ صَلَّى رَكْعَتَيْنِ