(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. (JA)
Reference (JA): Sahih Muslim 752 a (JA)
In-book reference (JA): Book 6, Hadith 186 (JA)
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 1641 (JA)