Musannaf Ibn Abi Shayba 3:3960

Ibn Idris narrated to us, from Hisham, from Ibn Sirin, from Aisha, that the Prophet (peace and blessings of Allah be upon him) used to recite in the two rak'ahs of the dawn [prayer]: "Say, 'O disbelievers'" and "Say, 'He is Allah, [who is] One.'"