Sahih Muslim Book 004, Hadith Number 1676.
Chapter : Encouragement to observe prayers during Ramadhan and that is Tarawih.
Ibn 'Abbas reported that he spent a night in the house of his maternal aunt, Maimuna. The Messenger of Allah (may peace he upon him) got up at night and performed short ablution (taking water) from the water-skin hanging there. (Giving a description of the ablution Ibn 'Abbas said: It was short and performed with a little water.) I also got up and did the same as the Apostle of Allah (may peace be upon him) had done. I then came (to him) and stood on his left. He then made me go around to his right side. He then observed prayer and went to sleep till he began to snore. Bilal came to him and informed him about the prayer. He (the Holy Prophet) then went out and observed the dawn prayer without performing ablution. Sufyan said: It was a special (prerogative of the) Apostle of Allah (may peace be upon him) for it has been conveyed to us that the eyes of the Apostle of Allah (may peace be upon him) sleep, but his heart does not sleep.