Sunan Abi Dawud Book 5, Hadith 9
The Prophet (ﷺ) said: Do not omit them (the two rak'ahs before the dawn prayer) even if you are driven away by the horses.
Ziyadah al-Kindi reported on the authority of Bilal that he (Bilal) came to the Messenger of Allah (ﷺ) to inform him about the dawn prayer. Aisha kept Bilal engaged in a matter which she asked him till the day was bright and it became fairly light. Bilal then stood up and called him to prayer and called him repeatedly. The Messenger of Allah (ﷺ) did not yet come out. When he came out, he led the people in prayer and he (Bilal) informed him that Aisha had kept him engaged in a matter which she asked him till it became fairly light; hence he became late in reaching him (in time). He (Bilal) said: Messenger of Allah, the dawn became fairly bright. He said: If the dawn became brighter than it is now, I would pray them (the two rak'ahs of the sunnah prayer), offer them well and in a more beautiful manner.
The Messenger of Allah (ﷺ) used to recite in both rak'ahs of the dawn prayer: "Say: We believe in Allah and in the revelation given to us" (3:84) . This is in the first rak'ah and in the second rak'ah (he recited): "We believe in Allah and bear witness that we submit ourself (to Him)." (3:52).