(14) باب اسْتِحْبَابِ رَكْعَتَيْ سُنَّةِ الْفَجْرِ وَالْحَثِّ عَلَيْهِمَا وَتَخْفِيفِهِمَا وَالْمُحَافَظَةِ عَلَيْهِمَا وَبَيَانِ مَا يُسْتَحَبُّ أَنْ يُقْرَأَ فِيهِمَا
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.
Reference: Sahih Muslim 723 a
In-book reference: Book 6, Hadith 106
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 1562