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 724 b
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".