Sahih Muslim
Sahih Muslim 724 b
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
وَحَدَّثَنِيهِ عَلِيُّ بْنُ حُجْرٍ، حَدَّثَنَا عَلِيٌّ يَعْنِي ابْنَ مُسْهِرٍ، ح وَحَدَّثَنَاهُ أَبُو كُرَيْبٍ، حَدَّثَنَا أَبُو أُسَامَةَ، ح وَحَدَّثَنَاهُ أَبُو بَكْرٍ، وَأَبُو كُرَيْبٍ وَابْنُ نُمَيْرٍ عَنْ عَبْدِ اللَّهِ بْنِ نُمَيْرٍ، ح وَحَدَّثَنَاهُ عَمْرٌو النَّاقِدُ، حَدَّثَنَا وَكِيعٌ، كُلُّهُمْ عَنْ هِشَامٍ، بِهَذَا الإِسْنَادِ وَفِي حَدِيثِ أَبِي أُسَامَةَ إِذَا طَلَعَ الْفَجْرُ
Translation
This hadith has been narrated by the same chain of transmitters and in the hadith narrated by Usama the words are
" When it was dawn".