Ali said: "Al-Witr is not incumbent like the status of the obligatory prayers, but it is a Sunnah which Allah's Messenger practiced."
Jami` at-Tirmidhi Book 3, Hadith 3
← Previous Hadith "Al-Witr is not incumbent like your obligatory prayers, but it is a Sunnah of Allah's Messenger who said: "Indeed Allah is Witr (One), and He loves Al-Witr, so perform Al-Witr O people of the Qur'an."

Jami` at-Tirmidhi Book 3, Hadith 2 Next Hadith → "Allah's Messenger ordered me to perform Al-Witr before sleeping."

Jami` at-Tirmidhi Book 3, Hadith 4