The Messenger of Allah ﷺ said: "Prayer at night is two by two, then when you want to finish, pray one rak'h which will make the total number that you prayed odd."  

عَنْ رَسُولِ اللَّهِ ﷺ قَالَ صَلاَةُ اللَّيْلِ مَثْنَى مَثْنَى فَإِذَا أَرَدْتَ أَنْ تَنْصَرِفَ فَارْكَعْ بِوَاحِدَةٍ تُوتِرُ لَكَ مَا قَدْ صَلَّيْتَ  

"The Messenger of Allah ﷺ said: 'Prayer at night is two by two, and witr is one rak'ah.'"  

قَالَ رَسُولُ اللَّهِ ﷺ صَلاَةُ اللَّيْلِ مَثْنَى مَثْنَى وَالْوَتْرُ رَكْعَةٌ وَاحِدَةٌ  

A man asked the Messenger of Allah ﷺ about prayer at night and the Messenger of Allah ﷺ said: "Prayer at night is two by two, then if one of you fears that dawn will break, pray one rak'ah to make the total number that he prayed odd."  

أَنَّ رَجُلاً سَأَلَ رَسُولَ اللَّهِ ﷺ عَنْ صَلاَةِ اللَّيْلِ فَقَالَ رَسُولُ اللَّهِ ﷺ صَلاَةُ اللَّيْلِ مَثْنَى مَثْنَى فَإِذَا خَشِيَ أَحَدُكُمُ الصُّبْحَ صَلَّى رَكْعَةً وَاحِدَةً تُوتِرُ لَهُ مَا قَدْ صَلَّى  

He heard the Messenger of Allah ﷺ say: "Prayer at night is two rak'ahs by two rak'ahs, then when you fear tat dawn will break, pray witr with one rak'ah."  

عَنْ رَسُولِ اللَّهِ ﷺ أَنَّهُ سَمِعَهُ يَقُولُ صَلاَةُ اللَّيْلِ رَكْعَتَيْنِ رَكْعَتَيْنِ فَإِذَا خِفْتُمُ الصُّبْحَ فَأَوْتِرُوا بِوَاحِدَةٍ  

The Prophet ﷺ used to pray eleven rak'ahs at night, ending them with one rak'ah of witr, then he would lie down on his right side.  

أَنَّ النَّبِيَّ ﷺ كَانَ يُصَلِّي مِنَ اللَّيْلِ إِحْدَى عَشْرَةَ رَكْعَةً يُوتِرُ مِنْهَا بِوَاحِدَةٍ ثُمَّ يَضْطَجِعُ عَلَى شِقِّهِ الأَيْمَنِ