A man from among the people of the desert asked the Messenger of Allah ﷺ about prayer at night. He said:"(It is) two by two, and Witr is one rak'ah at the end of the night."
أَنَّ رَجُلاً مِنْ أَهْلِ الْبَادِيَةِ سَأَلَ رَسُولَ اللَّهِ ﷺ عَنْ صَلاَةِ اللَّيْلِ قَالَ مَثْنَى مَثْنَى وَالْوَتْرُ رَكْعَةٌ مِنْ آخِرِ اللَّيْلِ