Ibn 'Umar (May Allah be pleased with them) reported:
The Prophet (ﷺ) performed the night prayer in pairs (i.e., Rak'ah) and made it odd number by observing one Rak'ah (as Witr).[Al-Bukhari and Muslim].
App reference: Book 9, Hadith 179
Arabic/English book reference: Book 9, Hadith 1169