Musnad Ahmad 5:423

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, from ‘Amr ibn Murrah, from Abu al-Bakhtari, from Abu ‘Abd al-Rahman al-Sulami, from ‘Ali, who said: "When a hadith is narrated to you from the Messenger of Allah (may Allah bless him and grant him peace), then think of the Messenger of Allah (may Allah bless him and grant him peace) as being the most righteous, the most God-fearing, and the most guided." And ‘Ali came out to us when the caller called for prayer, and he said: "Where is the one asking about the Witr? This is a time for a good Witr."