The Messenger of Allah ﷺ used to perform the witr prayer with three units. 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 يقرأ في الأولى: ب {سبح اسم ربك الأعلى} وفي الثانية ب {قل يأيها الكفرون} و في الثالثة ب {قل هو الله أحد}.
Nasai (1702) and Darimi (1596) both narrated it through the route of Abu Usama, who said, "Zakariya bin Abu Zaida told us, from Abu Ishaq, from Saeed bin Jubayr, from Ibn Abbas," and he related it. Its isnad is sahih. Yunus corroborated him in Ibn Majah (1172), as did Israil in Ahmad (2726) and Darimi (1632), and Sharik in Tirmidhi (462), all of them narrating from Abu Ishaq with the same wording. However, some of these narrators heard from Abu Ishaq at a late stage, such as Yunus bin Abu Ishaq, who heard from his father after he had become confused in his old age. Nawawi said in al-Khulasa (1885), "Tirmidhi, Nasai, and Ibn Majah narrated it with a sahih isnad." As for what Zuhayr bin Muawiya narrated from Abu Ishaq as a stopped report attributed only to Ibn Abbas, as Nasai narrated it, the evidence lies with whoever connected it.