Musnad Abu Ya'la al-Mawsili 150:120

Bishr ibn al-Walid narrated to us, Sharik narrated to us, from Yahya ibn Sa'id, from 'Amrah, from 'Aishah, who said: The Prophet (peace and blessings of Allah be upon him) used to pray the two rak'ahs before the dawn prayer and would lighten them, until I would think that he did not recite anything in them except the Opening of the Book (al-Fatihah), or that he did not recite the Opening of the Book.