(20) The Book of Qiyam Al-Lail (The Night Prayer) and Voluntary Prayers During the Day
كتاب قيام الليل وتطوع النهار
(41) Chapter: How to pray witr with five rak'ahs, and the differences reported from Al-Hakam in the hadith about Witr
(41) باب كَيْفَ الْوِتْرُ بِخَمْسٍ وَذِكْرِ الاِخْتِلاَفِ عَلَى الْحَكَمِ فِي حَدِيثِ الْوِتْرِ
Sunan an-Nasa'i 1717 
Hisham bin Urwah narrated from his father, from Aishah, that:
The Prophet (ﷺ) used to pray witr with five and he did not sit except in the last (rak'ah) of them.
أَخْبَرَنَا إِسْحَاقُ بْنُ مَنْصُورٍ، قَالَ أَنْبَأَنَا عَبْدُ الرَّحْمَنِ، عَنْ سُفْيَانَ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ، أَنَّ النَّبِيَّ صلى الله عليه وسلم كَانَ يُوتِرُ بِخَمْسٍ وَلاَ يَجْلِسُ إِلاَّ فِي آخِرِهِنَّ ‏.‏
Grade :  Sahih (Darussalam)
Reference : Sunan an-Nasa'i 1717
In-book reference : Book 20, Hadith 120
English translation : Vol. 2, Book 20, Hadith 1718