"Al-Witr is not incumbent like your obligatory prayers, but it is a Sunnah of Messenger of Allah who said: "Indeed Allah is Witr (One), and He loves Al-Witr, so perform Al-Witr O people of the Qur'an."  

الْوِتْرُ لَيْسَ بِحَتْمٍ كَصَلاَتِكُمُ الْمَكْتُوبَةِ وَلَكِنْ سَنَّ رَسُولُ اللَّهِ ﷺ وَقَالَ إِنَّ اللَّهَ وِتْرٌ يُحِبُّ الْوِتْرَ فَأَوْتِرُوا يَا أَهْلَ الْقُرْآنِ قَالَ وَفِي الْبَابِ عَنِ ابْنِ عُمَرَ وَابْنِ مَسْعُودٍ وَابْنِ عَبَّاسٍ  

“Witr is not definite (obligatory) nor is it like your prescribed prayers. But the Messenger of Allah ﷺ prayed Witr, then he said: ‘O people of the Qur’an! Perform Witr, for Allah is Witr* and He loves the odd (numbered).’” * Meaning 'one' which is the first of the odd numbers; He is unique, and there is nothing like Him, similar or equal.  

عَلِيُّ بْنُ أَبِي طَالِبٍ إِنَّ الْوِتْرَ لَيْسَ بِحَتْمٍ وَلاَ كَصَلاَتِكُمُ الْمَكْتُوبَةِ وَلَكِنْ رَسُولُ اللَّهِ ﷺ أَوْتَرَ ثُمَّ قَالَ يَا أَهْلَ الْقُرْآنِ أَوْتِرُوا فَإِنَّ اللَّهَ وِتْرٌ يُحِبُّ الْوِتْرَ  

‘Ali ؓ said: Verily, Witr is not a must like your prescribed prayers, but the Messenger of Allah ﷺ prayed Witr, then he said: “Pray Witr, O people of the Qurʿan. Pray Witr, for Allah is One and loves that which is odd numbered.” (Using translation from Aḥmad 1262)   

عَلِيٌّ إِنَّ الْوِتْرَ لَيْسَ بِحَتْمٍ كَصَلَاتِكُمُ الْمَكْتُوبَةِ وَلَكِنَّ رَسُولَ اللَّهِ ﷺ أَوْتَرَ ثُمَّ قَالَ «يَا أَهْلَ الْقُرْآنِ أَوْتِرُوا فَإِنَّ اللَّهَ وِتْرٌ يُحِبُّ الْوِتْرَ» وَمِنَ الشَّوَاهِدِ بِهَذَا الْحَدِيثِ مَا