Ibn Abdul-Rahman bin Abza reported,

...from his father, that the Messenger of Allah ﷺ used to pray witr with "Glorify the name of your Lord, the Most High" [Ala 87:1], "Say, you disbelievers" [Kafirun 109:1], and "Say, He is Allah, the One" [Ikhlas 112:1]. When he gave the closing salam he would say, "Glory be to the King, the Most Holy," three times, raising his voice on the third.

Azami 11073

Sahih

عن ابن عبد الرحمن بن أبز

ى، عن أبيه، أن رسول الله ﷺ كان يوتر ب {سبح اسم ربك الأعلى} و {قل يأيها الكفرون} و {قل هو الله أحد}. وكان يقول إذا سلم: سبحان الملك القدوس ثلاثا ويرفع صوته بالثالثة.

الأعظمي 11073صحيح
Contents
Reference
Commentary
Ayat
Collection
Jami al-Kamil
Book
Supplications, remembrances, and prayer upon the chosen Prophet ﷺ
Chapter
Supplications of adhan and prayer, and what is related to them
Section
What is recited in Witr prayer
Numbering
Jami al-Kamil 11073 (2nd edition)
Azami 11073