كتاب صلاة المسافرين وقصرها
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The Book of Prayer - Travellers
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Chapter: It is recommended to pray two rak`ah for the sunnah of Fajr. And encouragement to pray them regularly, and to make them brief, and to persist in offering them, and clarifying what is recommended to recite therein
(14)
باب اسْتِحْبَابِ رَكْعَتَيْ سُنَّةِ الْفَجْرِ وَالْحَثِّ عَلَيْهِمَا وَتَخْفِيفِهِمَا وَالْمُحَافَظَةِ عَلَيْهِمَا وَبَيَانِ مَا يُسْتَحَبُّ أَنْ يُقْرَأَ فِيهِمَا
Sahih Muslim 723 a

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.

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 ‏.‏
Reference : Sahih Muslim 723a
In-book reference : Book 6, Hadith 106
USC-MSA web (English) reference : Book 4, Hadith 1562
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