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
وَحَدَّثَنَاهُ مُحَمَّدُ بْنُ الْمُثَنَّى، حَدَّثَنَا ابْنُ أَبِي عَدِيٍّ، عَنْ هِشَامٍ، عَنْ يَحْيَى، عَنْ أَبِي سَلَمَةَ، عَنْ عَائِشَةَ، أَنَّ نَبِيَّ اللَّهِ صلى الله عليه وسلم كَانَ يُصَلِّي رَكْعَتَيْنِ بَيْنَ النِّدَاءِ وَالإِقَامَةِ مِنْ صَلاَةِ الصُّبْحِ .
'A'isha reported that the Messenger of Allah (ﷺ) used to observe two (supererogatory) rak'ahs in between the call to prayer and the Iqama of the dawn prayer.
Reference : Sahih Muslim 724cIn-book reference : Book 6, Hadith 113USC-MSA web (English) reference : Book 4, Hadith 1568