Musnad Ahmad 907:142

Abdullah narrated to us, Uthman ibn Muhammad narrated to me, Abu Dawud narrated to us, Sufyan narrated to us, from Simak ibn Harb, from Jabir ibn Samurah, who said: "When the Prophet, peace and blessings of Allah be upon him, prayed the dawn prayer, he would sit in his place of prayer and would not leave until the sun had risen."