Musnad Ahmad 907:165

Yahya ibn Adam narrated to us, from Zuhayr, from Simak, who said: I asked Jabir ibn Samurah about the prayer of the Messenger of Allah, peace and blessings of Allah be upon him. He said: "The Messenger of Allah, peace and blessings of Allah be upon him, used to recite in the Fajr [prayer] 'Qaf. By the Glorious Qur'an,' and [surahs] similar to it."