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 عَبْدِ اللَّهِ بْنِ عَبْدِ الْحَكَمِ، قَالَ أَنْبَأَنَا إِسْحَاقُ بْنُ الْفُرَاتِ، عَنْ يَحْيَى بْنِ أَيُّوبَ، قَالَ حَدَّثَنِي يَحْيَى بْنُ سَعِيدٍ، قَالَ أَنْبَأَنَا نَافِعٌ، عَنِ ابْنِ عُمَرَ، عَنْ حَفْصَةَ، أَنَّهَا أَخْبَرَتْهُ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ إِذَا نُودِيَ لِصَلاَةِ الصُّبْحِ سَجَدَ سَجْدَتَيْنِ قَبْلَ صَلاَةِ الصُّبْحِ .
It was narrated from Ibn 'Umar that Hafsah told him: "When he was called to Subh prayer, the Messenger of Allah (ﷺ) would do two prostrations before Subh prayer."
Reference : Sunan an-Nasa'i 1771In-book reference : Book 20, Hadith 174English translation : Vol. 2, Book 20, Hadith 1772