I asked 'Aishah: When would the Messenger of Allah ﷺ observe the witr prayer ? She replied: Any time he observed the witr, sometimes in the early hours of the night, sometimes at midnight and sometimes towards the end of it. But he used to observe the witr just before the dawn when he died.  

قُلْتُ لِعَائِشَةَ مَتَى كَانَ يُوتِرُ رَسُولُ اللَّهِ ﷺ قَالَتْ كُلَّ ذَلِكَ قَدْ فَعَلَ أَوْتَرَ أَوَّلَ اللَّيْلِ وَوَسَطَهُ وَآخِرَهُ وَلَكِنِ انْتَهَى وِتْرُهُ حِينَ مَاتَ إِلَى السَّحَرِ  

Make haste to observe the witr prayer before morning.  

أَنَّ النَّبِيَّ ﷺ قَالَ بَادِرُوا الصُّبْحَ بِالْوِتْرِ  

I asked 'Aishah about the witr observes by the Messenger of Allah ﷺ. She replied: Sometime he observed the witr prayer in the early hours of the night, sometimes he observed it at the end of it. I asked: How did he recite the Qur'an ? Did he recite the Qur'an quietly or loudly ? She replied: He did it in any way. Sometimes he recited quietly and sometimes loudly, sometimes he took bath and then slept and sometimes he performed ablution and then slept. Abu Dawud said: The narrators other than Qutaibah said: This refer to his bath due to sexual defilement.  

عَنْ وِتْرِ رَسُولِ اللَّهِ ﷺ قَالَتْ رُبَّمَا أَوْتَرَ أَوَّلَ اللَّيْلِ وَرُبَّمَا أَوْتَرَ مِنْ آخِرِهِ قُلْتُ كَيْفَ كَانَتْ قِرَاءَتُهُ أَكَانَ يُسِرُّ بِالْقِرَاءَةِ أَمْ يَجْهَرُ قَالَتْ كُلَّ ذَلِكَ كَانَ يَفْعَلُ رُبَّمَا أَسَرَّ وَرُبَّمَا جَهَرَ وَرُبَّمَا اغْتَسَلَ فَنَامَ وَرُبَّمَا تَوَضَّأَ فَنَامَ  

Make the last of your prayer at night a witr.  

عَنِ النَّبِيِّ ﷺ قَالَ اجْعَلُوا آخِرَ صَلاَتِكُمْ بِاللَّيْلِ وِتْرًا