كتاب صلاة المسافرين وقصرها
6  
The Book of Prayer - Travellers
(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
(14)
باب اسْتِحْبَابِ رَكْعَتَيْ سُنَّةِ الْفَجْرِ وَالْحَثِّ عَلَيْهِمَا وَتَخْفِيفِهِمَا وَالْمُحَافَظَةِ عَلَيْهِمَا وَبَيَانِ مَا يُسْتَحَبُّ أَنْ يُقْرَأَ فِيهِمَا
Sahih Muslim 727 b

Ibn 'Abbas reported that the Messenger of Allah (ﷺ) used to recite in the two (supererogatory) rak'ahs of the dawn prayer:

" Say: We believed in Allah and what was revealed to us" and that which is found in Surah Al-i-'lmran:" Come to that word (creed) which is common between you and us" (iii. 64).
وَحَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا أَبُو خَالِدٍ الأَحْمَرُ، عَنْ عُثْمَانَ بْنِ حَكِيمٍ، عَنْ سَعِيدِ بْنِ يَسَارٍ، عَنِ ابْنِ عَبَّاسٍ، قَالَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يَقْرَأُ فِي رَكْعَتَىِ الْفَجْرِ ‏{‏ قُولُوا آمَنَّا بِاللَّهِ وَمَا أُنْزِلَ إِلَيْنَا‏}‏ وَالَّتِي فِي آلِ عِمْرَانَ ‏{‏ تَعَالَوْا إِلَى كَلِمَةٍ سَوَاءٍ بَيْنَنَا وَبَيْنَكُمْ‏}
Reference : Sahih Muslim 727b
In-book reference : Book 6, Hadith 122
USC-MSA web (English) reference : Book 4, Hadith 1577
  (deprecated numbering scheme)