Musnad Ahmad 5:658

Abdullah narrated to us, Ishaq ibn Isma'il narrated to me, Jarir narrated to us, from Mansur, from Abu Ishaq, from 'Asim ibn Damrah, from 'Ali, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, Allah is Witr (Odd/One) and He loves the Witr. So perform Witr, O people of the Qur'an."