Yahya related to me from Malik from Nafi and Abdullah ibn Umarthat a man asked the Messenger of Allah, may Allah bless him and granthim peace, about night prayers. The Messenger of Allah, may Allahbless him and grant him peace, said, "Night prayers are two by two,and when you are afraid that dawn is approaching, pray one raka tomake what you have prayed odd."
App reference: Book 7, Hadith 13
USC-MSA web (English) reference: Book 7, Hadith 13
Arabic reference: Book 7, Hadith 267