Musnad Abu Ya'la al-Mawsili 248:19

Abu Bakr ibn Abi Shaybah narrated to us, Husayn ibn Ali narrated to us, from Za'idah, from Simak, from Jabir ibn Samurah, who said regarding the Prophet (peace and blessings of Allah be upon him): He used to recite in the Fajr [prayer] "Qaf. By the Glorious Qur'an." And his prayers after that were light.