Musnad Ahmad 1153:1511

'Abd al-Samad ibn 'Abd al-Warith narrated to us, he said: My father narrated to me, he said: Yahya—meaning Ibn Sa'id—narrated to me, he said: The nephew of 'Amrah narrated to me, from his paternal aunt 'Amrah, from 'Aishah, she said: "The Messenger of Allah, peace and blessings of Allah be upon him, used to pray the two rak'ahs before the dawn prayer, and he would lighten them so much that I would doubt whether he recited the Opening of the Book (Al-Fatihah) in them or not."