Musnad Ahmad 1153:1297

Ibn Numayr narrated to us, Yahya narrated to us, from Muhammad ibn Abd al-Rahman, from Amrah, from Aisha, who 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 say: 'Did he recite the Mother of the Quran [Al-Fatiha]?'"