صَحِيحُ مُسْلِمٍ
Sahih Muslim 723 d
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
وَحَدَّثَنَاهُ إِسْحَاقُ بْنُ إِبْرَاهِيمَ، أَخْبَرَنَا النَّضْرُ، حَدَّثَنَا شُعْبَةُ، بِهَذَا الإِسْنَادِ مِثْلَهُ .
A hadith like this has been narrated by Shu'ba with the same chain of transmitters.
Sahih Muslim, 723 dSahihصحيح