A man said, "O Messenger of Allah ﷺ! How is the prayer of the night?" He said, "Two rakʿat followed by two rakʿat and so on, and when you apprehend the approaching dawn, offer one rakʿa as witr." (Using translation from Bukhārī 1137)   

عَنِ النَّبِيِّ ﷺ قَالَ «صَلَاةُ اللَّيْلِ مَثْنَى مَثْنَى فَإِذَا خِفْتَ الصُّبْحَ فَأَوْتِرْ بِرَكْعَةٍ»  

A man stood up and said. Messenger of Allah, how is the night prayer? The Messenger of Allah ﷺ said: The night prayer consists of pair, but if you apprehend the rise of dawn, make it odd number by observing one rak'ah. (Using translation from Muslim 749c)   

أَخْبَرَهُ أَنَّ رَجُلًا سَأَلَ رَسُولَ اللهِ ﷺ كَيْفَ صَلَاةُ اللَّيْلِ؟ قَالَ «صَلَاةُ اللَّيْلِ مَثْنَى مَثْنَى فَإِذَا خِفْتَ الصُّبْحَ فَأَوْتِرْ بِرَكْعَةٍ»