(20) باب صَلاَةُ اللَّيْلِ مَثْنَى مَثْنَى وَالْوِتْرُ رَكْعَةٌ مِنْ آخِرِ اللَّيْلِ
Ibn 'Umar reported Allah's Messenger (ﷺ) as saying:
Witr is a rak'ah at the end of the prayer. (PT)
Reference (PT): Sahih Muslim 752 a (PT)
In-book reference (PT): Book 6, Hadith 186 (PT)
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 1641 (PT)