'Ali (bin Abu Talib) (May Allah be pleased with him) reported:
The Witr prayer is not obligatory as the prescribed Salat (prayers), but the Messenger of Allah ﷺ observed it as his regular practice (Sunnah). He ﷺ said, "Allah is Witr (single, odd) and loves what is Witr. So perform Witr prayer. O followers of Qur'an, observe Witr (prayer)."

[At-Tirmidhi and Abu Dawud].

عن علي رضي الله عنه قال: الوتر ليس بختم كصلاة المكتوبة ولكن سن رسول الله ﷺ قال: "إن الله وتر يحب الوتر، فأوتروا يا أهل القرآن". ((رواه أبو داود والترمذي)). وقال: حديث حسن.