It wasnarrated that Ibn 'Umar said:
"The Messenger of Allah (ﷺ)usedto pray (voluntary prayers) at night two by two, and he wouldprayone Rak'ah of Witr." (DE)
English reference (DE): Vol. 1, Book 5, Hadith 1174 (DE)
Arabic reference (DE): Book 5, Hadith 1230 (DE)