عَنِ ابْنِ عُمَرَ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «صَلَاةُ اللَّيْلِ مَثْنَى مَثْنَى فَإِذَا خَشِيَ أَحَدُكُمُ الصُّبْحَ صَلَّى رَكْعَةً وَاحِدَة توتر لَهُ مَا قد صلى»

He reported God’s Messenger as saying, “The witr* is a rak'a at the end of the night.” * Literally ‘single’, or ‘odd’, used of an odd number of rak'as prayed at some time during the night.Muslim transmitted it.