Full Sharh — Riyad as-Salihin 453

English Translation

'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).".