Musnad Abu Ya'la al-Mawsili 149:14

Shayban narrated to us, Abu 'Awanah narrated to us, from al-A'mash, from Abu al-Duha, from Masruq, who said: 'A'ishah said: "The Messenger of Allah (ﷺ) performed Witr at every time of the night, then his Witr ended at the time of the dawn (al-sahar)."