Musnad Abu Ya'la al-Mawsili 155:135

Muhammad ibn Jami‘ al-‘Attar narrated to us, Muhammad ibn ‘Uthman narrated to us, ‘Abd al-Salam ibn Abi al-Janub narrated to us, from Abu Salamah, from Abu Hurayrah, who said: The Messenger of Allah (ﷺ) recited before the dawn, then he recited six rak‘ahs, turning to the right and the left in every two rak‘ahs. We thought that for every seven [recitations] there were two rak‘ahs, and he did not say the taslim.