Sahih Muslim Book 4, Hadith Number 1634.

Chapter : Forenoon prayer should be offered when it is sufficiently hot.

‘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.