(20) باب صَلاَةُ اللَّيْلِ مَثْنَى مَثْنَى وَالْوِتْرُ رَكْعَةٌ مِنْ آخِرِ اللَّيْلِ
Ibn 'Umar said:
He who prayed at night should make Witr the end of his prayer, for the Messenger of Allah (ﷺ) ordered this. (ID)
Reference (ID): Sahih Muslim 751 a (ID)
In-book reference (ID): Book 6, Hadith 183 (ID)
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 1638 (ID)