Sahih Muslim 723aBook 6, Hadith 106
حَدَّثَنَا يَحْيَى بْنُ يَحْيَى، قَالَ قَرَأْتُ عَلَى مَالِكٍ عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، أَنَّ حَفْصَةَ أُمَّ الْمُؤْمِنِينَ، أَخْبَرَتْهُ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ إِذَا سَكَتَ الْمُؤَذِّنُ مِنَ الأَذَانِ لِصَلاَةِ الصُّبْحِ وَبَدَا الصُّبْحُ رَكَعَ 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.