The Prophet ﷺ used to recite in the Witr prayer "Glorify the name of your Lord, the Most High" [Ala 87:1], "Say, O 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. Glory be to the King, the Most Holy. Glory be to the King, the Most Holy," raising his voice with these words.
حدثنا محمد بن جعفر حدثنا شعبة عن سلمة بن كهيل وزبيد الإيامي عن ذر
عن النبي ﷺ أنه كان يقرأ في الوتر بسبح اسم ربك الأعلى وقل يا أيها الكافرون وقل هو الله أحد فإذا سلم قال سبحان الملك القدوس سبحان الملك القدوس سبحان الملك القدوس ورفع بها صوته
Its isnad is sahih, and all its narrators are reliable and firmly established. Ibn Abdul-Rahman is Saeed. Zayd Iyami, or Yami, is a reliable and firmly established narrator, well known. The hadith was reported by Abu Dawud 3/63, no. 1423, Nasai 3/244, no. 1729, and Tirmidhi 2/326, no. 462, who said, hasan gharib, and Ibn Majah 1/370, no. 1171. This is also the sourcing for the previous hadith.