Musnad Ahmad 922:6

Abdullah narrated to us, Uthman ibn Abi Shaybah narrated to us, Abu Hafs al-Abbar narrated to us, from al-A’mash, from Talhah and Zubayd, from Dharr, from Sa’id ibn Abd al-Rahman ibn Abza, from his father, from Ubayy ibn Ka’b: That the Messenger of Allah (may Allah bless him and grant him peace) used to perform Witr with "Glorify the name of your Lord, the Most High" (Surah Al-A’la), "Say, 'O disbelievers'" (Surah Al-Kafirun), and "Say, 'He is Allah, [who is] One'" (Surah Al-Ikhlas).