Musnad Ahmad 1153:742

'Abd al-Razzaq narrated to us, he said: Sufyan informed us, from al-A'mash, from Abu al-Duha, from Masruq, from 'A'ishah, she said: "The Messenger of Allah, may Allah bless him and grant him peace, performed the Witr prayer during every part of the night; he performed it in its beginning, its middle, and its end, and his Witr concluded at the time of the predawn (al-sahar)."