Musnad Abu Ya'la al-Mawsili 110:235

Zuhayr narrated to us, Qasim ibn Malik al-Muzani narrated to us, from Hanzalah ibn Abdullah al-Sadusi, from Shahr ibn Hawshab, from Ibn Abbas: That the Messenger of Allah (may Allah bless him and grant him peace) prayed two rak'ahs, in which he recited the Mother of the Book (Al-Fatiha), and he did not add anything to it.