وَعَنْ عَلِيِّ بْنِ أَبِي طَالِبٍ رضى الله عنه
قَالَ: «لَيْسَ اَلْوِتْرُ بِحَتْمٍ كَهَيْئَةِ اَلْمَكْتُوبَةِ، وَلَكِنْ سُنَّةٌ سَنَّهَا رَسُولُ اَللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ -»
The Witr prayer is not obligatory as the prescribed prayer is, but it is a Sunnah which was established by the practice of the Messenger of Allah (sallallahu alayhi wa sallam).
Bulugh al-Maram 450, Book 2, The Book of Prayer, Hadith 271. 1 min read