Al-Mundhiri records in his book al-Targhib wal-Tarhib:

الترغيب في صلاة الوتر

Encouragement to perform the Witr prayer.

Source: al-Targhīb wal-Tarhīb 1/229

Ali ibn Abi Talib reported: The Messenger of Allah, peace and blessings be upon him, said:

إِنَّ اللَّهَ وِتْرٌ يُحِبُّ الْوِتْرَ فَأَوْتِرُوا يَا أَهْلَ الْقُرْآنِ

Verily, Allah is numerically odd and He loves what is odd. Perform the Witr prayer, O people of the Quran!

Ali said:

الْوِتْرُ لَيْسَ بِحَتْمٍ كَصَلَاتِكُمْ الْمَكْتُوبَةِ وَلَكِنْ سَنَّ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ

The Witr prayer is not required like your prescribed prayers, but it is the Sunnah of the Messenger of Allah, peace and blessings be upon him.

Source: Sunan al-Tirmidhī 453, Grade: Sahih

Jabir reported: The Messenger of Allah, peace and blessings be upon him, said:

مَنْ خَافَ أَنْ لَا يَقُومَ مِنْ آخِرِ اللَّيْلِ فَلْيُوتِرْ أَوَّلَهُ وَمَنْ طَمِعَ أَنْ يَقُومَ آخِرَهُ فَلْيُوتِرْ آخِرَ اللَّيْلِ فَإِنَّ صَلَاةَ آخِرِ اللَّيْلِ مَشْهُودَةٌ وَذَلِكَ أَفْضَلُ

Whoever fears he cannot stand for prayer at the end of the night, let him perform Witr prayer in its beginning. Whoever hopes to stand for prayer at the end of the night, let him perform Witr prayer at its ending. Verily, prayer at the end of the night is witnessed, and that is better.

Source: Ṣaḥīḥ Muslim 755, Grade: Sahih

Abu Huraira reported: The Prophet, peace and blessings be upon him, said:

إِنَّ اللهَ وِتْرٌ يُحِبُّ الْوِتْرَ

Verily, Allah is numerically odd and He loves what is odd in number.

Source: Ṣaḥīḥ Muslim 2677, Grade: Sahih

Abu Basrah reported: The Prophet, peace and blessings be upon him, said:

إِنَّ اللهَ عَزَّ وَجَلَّ زَادَكُمْ صَلَاةً فَصَلُّوهَا فِيمَا بَيْنَ صَلَاةِ الْعِشَاءِ إِلَى صَلَاةِ الصُّبْحِ الْوَتْرُ الْوَتْرُ

Verily, Allah Almighty has added one to your prayers, so perform it between the evening and dawn prayers: the Witr prayer, the Witr prayer.

Source: Musnad Aḥmad 27229, Grade: Sahih

Abu Ayyub reported: The Messenger of Allah, peace and blessings be upon him, said:

الْوِتْرُ حَقٌّ عَلَى كُلِّ مُسْلِمٍ فَمَنْ أَحَبَّ أَنْ يُوتِرَ بِخَمْسٍ فَلْيَفْعَلْ وَمَنْ أَحَبَّ أَنْ يُوتِرَ بِثَلَاثٍ فَلْيَفْعَلْ وَمَنْ أَحَبَّ أَنْ يُوتِرَ بِوَاحِدَةٍ فَلْيَفْعَلْ

The Witr prayer is a duty upon every Muslim. Whoever likes to pray it with five cycles, let him do so. Whoever likes to pray it with three cycles, let him do so. Whoever likes to pray it with one cycle, let him do so.

Source: Sunan Abī Dāwūd 1422, Grade: Sahih

Aisha reported:

مِنْ كُلِّ اللَّيْلِ قَدْ أَوْتَرَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ مِنْ أَوَّلِ اللَّيْلِ وَأَوْسَطِهِ وَآخِرِهِ فَانْتَهَى وِتْرُهُ إِلَى السَّحَرِ

The Messenger of Allah, peace and blessings be upon him, would perform Witr prayer every night, sometimes at the beginning, middle, or end of the night, finishing his Witr prayer until an hour before dawn.

Source: Ṣaḥīḥ al-Bukhārī 996, Grade: Muttafaqun Alayhi