"In the first rak'ah of witr, the Messenger of Allah ﷺ used to recite: "GLorify the Name of your Lord, the Most High;" in the second; "Say: O you disbelievers!" and in the third; "Say: He is Allah, (the) One." (Using translation from Nasāʾī 1700)   

كَانَ النَّبِيُّ ﷺ يُوتِرُ بِثَلَاثٍ يَقْرَأُ فِي الْأُولَى بِسَبِّحِ اسْمَ رَبِّكَ الْأَعْلَى وَفِي الثَّانِيَةِ بِقُلْ يَا أَيُّهَا الْكَافِرُونَ وَفِي الثَّالِثَةِ بِقُلْ هُوَ اللَّهُ أَحَدٌ