Musnad Ahmad 1153:670

Muhammad ibn Ja‘far narrated to us, he said: Shu‘bah narrated to us, from Muhammad ibn ‘Abd al-Rahman, from his paternal aunt ‘Amrah, from ‘Aishah, that she said: "When the dawn would break, the Messenger of Allah (peace and blessings of Allah be upon him) would pray two rak‘ahs, or he would not pray except two rak‘ahs. I say: He would recite in them the Opening of the Book (Fatihat al-Kitab)."