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]. (ID)
App reference (ID): Book 9, Hadith 179 (ID)
Arabic/English book reference (ID): Book 9, Hadith 1169 (ID)