In the name of Allah, the Gracious, the Merciful
Al-Nawawi records in his book Riyad al-Salihin:
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 odd and he loves what is odd, so perform the witr prayer, O people of the Quran!
Ali, may Allah be pleased with him, 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
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, at the beginning, middle, or end of the night, performing witr prayer at dawn.
Source: Ṣaḥīḥ al-Bukhārī 951, Grade: Muttafaqun Alayhi
Abdullah ibn Umar reported: The Prophet, peace and blessings be upon him, said:
اجْعَلُوا آخِرَ صَلَاتِكُمْ بِاللَّيْلِ وِتْرًا
Make the last of your prayers at night the witr prayer.
Source: Ṣaḥīḥ al-Bukhārī 953, Grade: Muttafaqun Alayhi
Abu Sa’id al-Khudri reported: The Prophet, peace and blessings be upon him, said:
أَوْتِرُوا قَبْلَ أَنْ تُصْبِحُوا
Perform witr prayer before the morning.
Source: Ṣaḥīḥ Muslim 754, 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
Success comes from Allah, and Allah knows best.