Whoever prays during the night should make the last of his prayer the witr, for the Messenger of Allah ﷺ used to command this.
أخبرنا قتيبة قال حدثنا الليث عن نافع أن
من صلى من الليل فليجعل آخر صلاته وترا فإن رسول الله ﷺ كان يأمر بذلك
Muslim narrated it in the book of the Prayer of the Traveler, chapter on the night prayer being performed two units at a time and so on, hadith no. 751, from Qutayba.Bukhari narrated it in the book of Witr, chapter on making the last of one's prayer a witr, hadith no. 998, from the hadith of Nafi with the same wording. It is also found in Kubra, hadith no. 1391.Layth is Ibn Saad.