The Messenger of Allah ﷺ used to perform witr with three rakahs. In the first he would recite "Glorify the name of your Lord, the Most High" [Ala 87:1], in the second "Say, O disbelievers" [Kafirun 109:1], and in the third "Say, He is Allah, the One" [Ikhlas 112:1].
كان رسول الله ﷺ يوتر بثلاث، يقرأفي الأولى ب{سبح اسم ربك الأعلى}، وفي الثانية ب{قل يأيها الكفرون}، و في الثالثة {قل هو الله أحد}.
Nasai (1702) and Darimi (1596) both narrated it through Abu Usama, who said, "Zakariya bin Abu Zaida told us, from Abu Ishaq, from Saeed bin Jubayr, from Ibn Abbas," and he mentioned it. This is a sahih chain of transmission. The discussion of it is given in detail in the Book of Prayer. There are other hadiths on this same subject mentioned in the Book of Prayer.