The Book of Qiyam Al-Lail (The Night Prayer) and Voluntary Prayers During the Day
20/60. Chapter:
The time for the two rak'ahs of Fajr, and mentioning the differences reported from Nafi'
Sunan an-Nasai
أَخْبَرَنَا مُحَمَّدُ بْنُ سَلَمَةَ، قَالَ أَنْبَأَنَا ابْنُ الْقَاسِمِ، عَنْ مَالِكٍ، قَالَ حَدَّثَنِي نَافِعٌ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ، أَنَّ حَفْصَةَ أُمَّ الْمُؤْمِنِينَ، أَخْبَرَتْهُ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ إِذَا سَكَتَ الْمُؤَذِّنُ مِنَ الأَذَانِ لِصَلاَةِ الصُّبْحِ وَبَدَا الصُّبْحُ صَلَّى رَكْعَتَيْنِ خَفِيفَتَيْنِ قَبْلَ أَنْ تُقَامَ الصَّلاَةُ .
It was narrated from 'Abdullah bin Umar that Hafsah, the Mother of the Believers, told him: 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.
Reference : Sunan an-Nasa'i 1773In-book reference : Book 20, Hadith 176English translation : Vol. 2, Book 20, Hadith 1774