Abu Dawud Book 2, Hadith Number 1418.
Chapter : What is recited in the witr.
Narated By Ubayy ibn Ka’b : The Apostle of Allah (PBUH) used to observe witr with (reciting) “Glorify the name of thy Lord, the most High” (Surah 87), “Say O disbelievers” (Surah 109), and “Say, He is Allah, the One, Allah, the eternally besought of all” (112).