Musnad Ahmad 5:314

Ali ibn Bahr narrated to us, Isa ibn Yunus narrated to us, Zakariya narrated to us, from Abu Ishaq, from Asim ibn Damrah, from Ali, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "O people of the Quran, perform the Witr prayer, for Allah, the Almighty and Majestic, is Witr (One/Odd) and He loves the Witr."