صَحِيحُ مُسْلِمٍ
Sahih Muslim 749 d
The Book of Prayer - Travellers
The night prayers are two by two, and Witr is one rakah at the end of the night
وَحَدَّثَنِي أَبُو الرَّبِيعِ الزَّهْرَانِيُّ، حَدَّثَنَا حَمَّادٌ، حَدَّثَنَا أَيُّوبُ، وَبُدَيْلٌ، عَنْ عَبْدِ اللَّهِ بْنِ شَقِيقٍ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ، أَنَّ رَجُلاً، سَأَلَ النَّبِيَّ صلى الله عليه وسلم وَأَنَا بَيْنَهُ وَبَيْنَ السَّائِلِ فَقَالَ يَا رَسُولَ اللَّهِ كَيْفَ صَلاَةُ اللَّيْلِ قَالَ مَثْنَى مَثْنَى فَإِذَا خَشِيتَ الصُّبْحَ فَصَلِّ رَكْعَةً وَاجْعَلْ آخِرَ صَلاَتِكَ وِتْرًا . ثُمَّ سَأَلَهُ رَجُلٌ عَلَى رَأْسِ الْحَوْلِ وَأَنَا بِذَلِكَ الْمَكَانِ مِنْ رَسُولِ اللَّهِ صلى الله عليه وسلم فَلاَ أَدْرِي هُوَ ذَلِكَ الرَّجُلُ أَوْ رَجُلٌ آخَرُ فَقَالَ لَهُ مِثْلَ ذَلِكَ .
'Abdullah b. 'Umar reported: A person asked the Messenger of Allah (ﷺ) as I stood between him (the Prophet) and the inquirer and he said: Messenger of Allah, how is the night prayer? He (the Prophet) said: It consists of pairs of rak'ahs, but if you apprehend morning, you should pray one rak'ah and make the end of your prayer as Witr. Then a person asked him (the Prophet) at the end of the year and I was at that place near the Messenger of Allah (ﷺ) ; but I do not know whether he was the same person or another person, but he (the Prophet) gave him the same reply.
Sahih Muslim, 749 dSahihصحيح