A man who lived in the desert asked the Messenger of Allah ﷺ about the prayer at night. He made a sign with his two fingers-in this way in pairs. The witr consists of one rak'ah towards the end in night.  

أَنَّ رَجُلاً مِنْ أَهْلِ الْبَادِيَةِ سَأَلَ النَّبِيَّ ﷺ عَنْ صَلاَةِ اللَّيْلِ فَقَالَ بِأُصْبُعَيْهِ هَكَذَا مَثْنَى مَثْنَى وَالْوِتْرُ رَكْعَةٌ مِنْ آخِرِ اللَّيْلِ  

The Prophet ﷺ said: The witr is a duty for every Muslim so if anyone wishes to observe it with five rak'ahs, he may do so; if anyone wishes to observe it with three, he may do so, and if anyone wishes to observe it with one, he may do so.  

قَالَ رَسُولُ اللَّهِ ﷺ الْوِتْرُ حَقٌّ عَلَى كُلِّ مُسْلِمٍ فَمَنْ أَحَبَّ أَنْ يُوتِرَ بِخَمْسٍ فَلْيَفْعَلْ وَمَنْ أَحَبَّ أَنْ يُوتِرَ بِثَلاَثٍ فَلْيَفْعَلْ وَمَنْ أَحَبَّ أَنْ يُوتِرَ بِوَاحِدَةٍ فَلْيَفْعَلْ