Musannaf Ibn Abi Shayba 3:4495

Abu Bakr narrated to us, he said: Hushaym narrated to us, he said: ‘Abd al-Malik informed us, from Zubayd, from Sa‘id ibn ‘Abd al-Rahman ibn Abza, from his father, that the Messenger of Allah (may Allah bless him and grant him peace) used to recite in his Witr: "Glorify the name of your Lord, the Most High," and "Say, 'O disbelievers,'" and "Say, 'He is Allah, [who is] One.'" And when he would say the taslim, he would say: "Glory be to You, the Sovereign, the Holy," three times.