The Book of Prayers (Kitab Al-Salat)
Muslim :: Book 4 : Hadith 1576
Ibn 'Abbas reported that the Messenger of Allah (may peace be upon him) used to recite in first of the two (supererogatory) rak'ahs of the dawn:" Say: We believed in Allah and what was revealed to us..." verses 285-286 from Surah Baqara, and in the second of the two:" I believe in Allah and I bear testimony that we are Muslims" (iii. 51).