Musannaf Ibn Abi Shayba 3:4511

Muhammad ibn Ubaydah narrated to us, he said: My father narrated to me, from al-A’mash, from Talhah, from Zirr, from Sa’id ibn Abd al-Rahman ibn Abza, from his father, from Ubayy ibn Ka’b, that the Prophet (peace and blessings of Allah be upon him) used to perform Witr with "Glorify the name of your Lord, the Most High," and "Say, 'O disbelievers,'" and "Say, 'He is Allah, [who is] One.'" And he would say at the end of his prayer, "Exalted is the Sovereign, the Holy," three times.