Musnad Ahmad 907:38

Abu Kamil narrated to us, Zuhayr narrated to us, Simak ibn Harb narrated to us, he said: I asked Jabir about the prayer of the Prophet, may God bless him and grant him peace, and he said: "He used to lighten [it], and he would not pray the prayer of these [people]." He said: And he informed me "that the Messenger of God, may God bless him and grant him peace, used to recite in the dawn [prayer]: 'Qaf. By the Glorious Qur'an' and the like of it."