Riyad as-Salihin, Book 9, Hadith 1169 (In-Book) ⓘ
Ibn 'Umar (May Allah be pleased with them) reported: The Prophet 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].
وعنه قال: كان النبي صلى الله عليه وسلم ، يصلي من الليل مثنى مثنى، ويوتر بركعة. ((متفق عليه)) .