Sahih Muslim
The Book of Prayers (Kitab Al-Salat)
Book Number: 004 / Hadith Number: 1634
'Abdullah b. 'Umar reported: A man stood up and said. Messenger of Allah, how is the night prayer? The Messenger of Allah (may peace be upon him) said: The night prayer consists of pair, but if you apprehend the rise of dawn, make it odd number by observing one rak'ah.