Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said that a man asked the Messenger of Allah (peace and blessings be upon him) about the night prayer, and he (peace and blessings be upon him) said: "The night prayer is two rak'ahs at a time. When one of you fears (the approach of) the morning, let him pray one rak'ah, which will make what he has prayed odd (witr)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4570
Abdullah bin Umar (may Allah be pleased with them both) said that the Messenger of Allah (peace and blessings be upon him) said: "The night prayer is two rak'ahs at a time. When you sense that the morning is about to overtake you, then pray witr with one rak'ah." A man asked Ibn Umar (may Allah be pleased with them both): What is meant by "two"? He said: Saying the salam after every two rak'ahs.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4571
Urwah bin al-Zubayr narrates from Sayyidah Aishah (may Allah be pleased with her) that the Prophet (peace and blessings be upon him), after finishing the Isha prayer until Fajr, used to pray eleven rak'ahs, (praying) one rak'ah as witr, and he would make his prostration as long as it takes one of you to recite fifty verses. When the muezzin fell silent from the Fajr adhan and the dawn became clear, he (peace and blessings be upon him) would pray two light rak'ahs, then lie down on his right side until the muezzin came for the iqamah, and he (peace and blessings be upon him) would go out with him. Some of them narrated something more as well.
(b) Yunus bin Yazid states that he would say the salam after every two rak'ahs.
(c) Al-Zuhri states: When the muezzin intended to give the first adhan of Fajr.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4572