The son of Abd al-Rahman bin Abza narrates from his father, Sayyiduna Abd al-Rahman bin Abza (may Allah be pleased with him), that the Prophet (peace and blessings be upon him) used to recite in witr "Glorify the name of your Lord, the Most High" [Surah al-A'la: 1], "Say: O disbelievers" [Surah al-Kafirun: 1] and "Say: He is Allah, the One" [Surah al-Ikhlas: 1], and when he gave the salam he would say: 'Subhan al-Malik al-Quddus' (Glory be to the King, the Most Holy) three times, raising his voice the third time.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4869
Ubayy bin Ka'b (may Allah be pleased with him) said that when the Messenger of Allah (peace and blessings be upon him) gave the salam at the end of witr, he would say: 'Subhan al-Malik al-Quddus' (Glory be to the King, the Most Holy).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4870
Abd al-Rahman bin al-Harith bin Hisham narrates from Sayyiduna Ali (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) used to make this supplication at the end of his witr:
'Allahumma inni a'udhu bi-ridaka min sakhatik, wa bi-mu'afatika min 'uqubatik, wa a'udhu bika mink, la uhsi thana'an 'alayk, anta kama athnayta 'ala nafsik'
(O Allah, I seek refuge in Your pleasure from Your anger, and in Your pardon from Your punishment, and I seek refuge in You from You. I cannot enumerate Your praise; You are as You have praised Yourself.)
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4871