ʿAllah is One and loves that which is odd numbered, so pray Witr, O people of the Qur’an.” (Using translation from Aḥmad 1225)  

قَالَ رَسُولُ اللهِ ﷺ «إِنَّ» اللهَ وُتِرٌ يُحِبُّ الْوِتْرَ فَأَوْتِرُوا يَا أَهْلَ الْقُرْآنِ  

Witr is not a must like the obligatory prayers, but it is a Sunnah established by the Messenger of Allah ﷺ. (Using translation from Aḥmad 927)   

«لَيْسَ الْوِتْرُ بِحَتْمٍ مِثْلَ الْمَكْتُوبَةِ وَلَكِنَّهُ سُنَّةٌ سَنَّهَا رَسُولُ اللهِ ﷺ»