I heard the Messenger of Allah ﷺ say: The witr is a duty, so he who does not observe it does not belong to us; the witr is a duty, so he who does not observe it does not belong to us; the witr is a duty, so he who does not observe it does not belong to us.  

سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ الْوِتْرُ حَقٌّ فَمَنْ لَمْ يُوتِرْ فَلَيْسَ مِنَّا الْوِتْرُ حَقٌّ فَمَنْ لَمْ يُوتِرْ فَلَيْسَ مِنَّا الْوِتْرُ حَقٌّ فَمَنْ لَمْ يُوتِرْ فَلَيْسَ مِنَّا  

Ibn Muhayriz said: A man from Banu Kinanah, named al-Makhdaji, heard a person called AbuMuhammad in Syria, saying: The witr is a duty (wajib). Al-Makhdaji said: So I went to Ubadah ibn as-Samit and informed him. Ubadah said: AbuMuhammad told a lie. I heard the Messenger of Allah ﷺ say: There are five prayers which Allah has prescribed on His servants. If anyone offers them, not losing any of them, and not treating them lightly, Allah guarantees that He will admit him to Paradise. If anyone does not offer them, Allah does not take any responsibility for such a person. He may either punish him or admit him to Paradise.  

سَمِعَ رَجُلاً بِالشَّامِ يُدْعَى أَبَا مُحَمَّدٍ يَقُولُ إِنَّ الْوِتْرَ وَاجِبٌ قَالَ الْمُخْدَجِيُّ فَرُحْتُ إِلَى عُبَادَةَ بْنِ الصَّامِتِ فَأَخْبَرْتُهُ فَقَالَ عُبَادَةُ كَذَبَ أَبُو مُحَمَّدٍ سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ خَمْسُ صَلَوَاتٍ كَتَبَهُنَّ اللَّهُ عَلَى الْعِبَادِ فَمَنْ جَاءَ بِهِنَّ لَمْ يُضَيِّعْ مِنْهُنَّ شَيْئًا اسْتِخْفَافًا بِحَقِّهِنَّ كَانَ لَهُ عِنْدَ اللَّهِ عَهْدٌ أَنْ يُدْخِلَهُ الْجَنَّةَ وَمَنْ لَمْ يَأْتِ بِهِنَّ فَلَيْسَ لَهُ عِنْدَ اللَّهِ عَهْدٌ إِنْ شَاءَ عَذَّبَهُ وَإِنْ شَاءَ أَدْخَلَهُ الْجَنَّةَ