Sahih Muslim
Sahih Muslim 725 a
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
Arabic hadith text
حَدَّثَنَا مُحَمَّدُ بْنُ عُبَيْدٍ الْغُبَرِيُّ، حَدَّثَنَا أَبُو عَوَانَةَ، عَنْ قَتَادَةَ، عَنْ زُرَارَةَ بْنِ أَوْفَى، عَنْ سَعْدِ بْنِ هِشَامٍ، عَنْ عَائِشَةَ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ "رَكْعَتَا الْفَجْرِ خَيْرٌ مِنَ الدُّنْيَا وَمَا فِيهَا "
Translation
'A'isha reported Allah's Messenger as saying
The two rak'ahs at dawn are better than this world and what it contains.