The Messenger of Allah ﷺ used to recite in the Witr "Glorify the name of your Lord, the Most High" [Ala 87:1], in the second rakat "Say, you disbelievers" [Kafirun 109:1], and in the third "Say, He is Allah, the One" [Ikhlas 112:1]. He would give the closing salutation only at the end of them, and then, after the salutation, he would say three times, "Glory be to the King, the Most Holy."
كان رسول الله ﷺ يقرأ في الوتر ب {سبح اسم ربك الأعلى}. وفي الركعة الثانية ب {قل يأيها الكفرون} وفي الثالثة ب {قل هو الله أحد} ولا يسلم إلا في آخرهن، ويقول: يعني بعد التسليم: سبحان الملك القدوس ثلاثا.
Nasai (1701) narrated it from Yahya bin Musa, who said, Abdul-Aziz bin Khalid informed us, who said, Saeed bin Abu Aruba narrated to us, from Qatada, from Azra, from Saeed bin Abdul-Rahman bin Abza, from his father, from Ubayy bin Kaab, and he mentioned it. Its chain of transmission is sahih.