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." (JA)
English reference (JA): Vol. 1, Book 5, Hadith 1174 (JA)
Arabic reference (JA): Book 5, Hadith 1230 (JA)