C33 · Sahih Muslim - The Book of Prayer - Travellers, Hadith 751 (Grade: Sahih - Authentic)
أَنَّ ابْنَ عُمَرَ، قَالَ مَنْ صَلَّى مِنَ اللَّيْلِ فَلْيَجْعَلْ آخِرَ صَلاَتِهِ وِتْرًا فَإِنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ يَأْمُرُ بِذَلِكَ
Ibn 'Umar said: He who prayed at night should make Witr the end of his prayer, for the Messenger of Allah (ﷺ) ordered this.
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