Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said: I heard a man asking the Prophet (peace and blessings be upon him), while he (peace and blessings be upon him) was on the pulpit: "How should one of us pray at night?" He (peace and blessings be upon him) said: "Two rak'ahs at a time; then when you fear the arrival of the morning, pray one more rak'ah to make the prayer you have offered odd (witr)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4765