The Book of Prayer - Travellers
6/14. 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
Sahih Muslim
حَدَّثَنِي مُحَمَّدُ بْنُ عَبَّادٍ، وَابْنُ أَبِي عُمَرَ، قَالاَ حَدَّثَنَا مَرْوَانُ بْنُ مُعَاوِيَةَ، عَنْ يَزِيدَ، - هُوَ ابْنُ كَيْسَانَ - عَنْ أَبِي حَازِمٍ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَرَأَ فِي رَكْعَتَىِ الْفَجْرِ { قُلْ يَا أَيُّهَا الْكَافِرُونَ} وَ { قُلْ هُوَ اللَّهُ أَحَدٌ}
Abu Huraira reported that the Messenger of Allah (ﷺ) recited in the two (supererogatory) rak'ahs of the dawn (prayer): " Say: O unbelievers," (Qur'an, cix.) and" Say: Allah is one" (cxii.).
Reference : Sahih Muslim 726In-book reference : Book 6, Hadith 120USC-MSA web (English) reference : Book 4, Hadith 1575