Musannaf Ibn Abi Shayba 3:1364

Yazid ibn Harun narrated to us, from Hammam and Aban al-Attar, from Yahya ibn Abi Kathir, from Abdullah ibn Abi Qatadah, from his father, that the Prophet, peace and blessings of Allah be upon him, used to recite in the first two rak'ahs the Opening of the Book (Al-Fatiha) and a surah, and in the last two (he would recite) the Opening of the Book.