Musnad Ahmad 5:648

'Abdullah narrated to us, 'Ubaydullah ibn 'Umar al-Qawariri narrated to me, Yazid ibn Zuray' narrated to me, Shu'bah narrated to me, from Abu Ishaq, from 'Asim ibn Damrah, from 'Ali, who said: "The Messenger of Allah (ﷺ) performed the Witr prayer during every part of the night: in its beginning, its middle, and its end. And his Witr concluded at the end of the night."