Musnad Ahmad 1153:1872

'Abd al-Razzaq narrated to us, he said: Hisham informed us, from Muhammad, from 'Aishah, she said: The Prophet, may Allah bless him and grant him peace, recited silently in the two rak'ahs of the dawn prayer, and he recited in them "Say, 'O disbelievers'" and "Say, 'He is Allah, [who is] One.'"