Abdullah bin Shaqiq (may Allah have mercy on him) narrates from Sayyiduna Ibn Umar (may Allah be pleased with them both) that a man asked the Prophet (peace and blessings be upon him) while I was between the Prophet (peace and blessings be upon him) and the questioner. He said: O Messenger of Allah! How is the night prayer (to be offered)? He (peace and blessings be upon him) said: "Two by two rak'ahs; when you fear (the coming of) the morning, pray one rak'ah, and make witr your last prayer." Then, a year later, a man asked the Prophet (peace and blessings be upon him) at the same place; I do not know whether it was the same man or someone else, and he (peace and blessings be upon him) told him the same thing.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4830