Musnad Ahmad 1153:674

Muhammad ibn Ja'far narrated to us, he said: Shu'bah narrated to us, from Sulayman, he said: I heard Abu al-Duha narrating from Masruq, from 'Aishah, that she said: "The Messenger of Allah, peace and blessings of Allah be upon him, performed the Witr prayer during every part of the night, and his Witr settled at the time of the dawn (al-sahar)."