Sunan Ibn Majah, Chapter: The Chapters of Establishing the Prayer and the Sunnah Regarding Them

"We asked Aishah what the Messenger of Allah (saw) used to recite in Witr. She said: 'He used to recite: "Glorify the Name of your Lord the Most High," [Al-A'la (87)] in the first Rakah, 'Say: "O disbelievers!'" [Al- Kafirun (109)] in the second Rakah, and 'Say: Allah is One' in the third and the Mu'awwidhatain (Chapter 113, 114).'" Sahih