Abu Dawud Book 2, Hadith Number 1254.
Chapter : On observing the sunan prayer at dawn lightly.
Narated By ‘Abd Allah b. ‘Abbas : The Apostle of Allah (PBUH) used to recite in both rak’ahs of the dawn prayer: “Say: We believe in Allah and in the revelation given to us” (ii. 136). This is in the first rak’ah; and in the second rak’ah (he recited): “We believe in Allah and bear thou witness that we are submitting ones” (iii. 51).