Sayyiduna Abdullah bin Umar (may Allah be pleased with them) narrates that the Prophet Muhammad (peace and blessings be upon him) said: The night prayer is in sets of two rak'ahs. When you fear that dawn is approaching, then perform one rak'ah as witr. In the narration of Mahmood, it is stated: It will make your previous prayer an odd number (witr).
Hadith Referenceالمنتقى ابن الجارود / كتاب الصلاة / 267
Hadith Gradingغلام مصطفےٰ ظهير امن پوري:صحيح
Hadith Takhrijاز غلام مصطفےٰ ظهير امن پوري:«صحيح البخاري : 1137 ، صحيح مسلم : 749/147»