الْوِتْرُ لَيْسَ بِحَتْمٍ كَهَيْئَةِ الْمَكْتُوبَةِ وَلَكِنَّهُ سُنَّةٌ سَنَّهَا رَسُولُ اللَّهِ صلى الله عليه وسلم .
It was narrated that Ali, may Allah (SWT) be pleased with him, said: "Witr is not essential like the obligatory prayers, but it is the sunnah of the Messenger of Allah (ﷺ)."