Sahih Muslim 726
Sahih Muslim · Book 6: The Book of Prayer - Travellers · 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
Abu Huraira reported that the Messenger of Allah (ﷺ) recited in the two (supererogatory) rak'ahs of the dawn (prayer):
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}
" Say: O unbelievers," (Qur'an, cix.) and" Say: Allah is one" (cxii.).