Sahih Muslim Book 4, Hadith Number 1674.

Chapter : Encouragement to observe prayers during Ramadhan and that is Tarawih.

Ibn Abbas reported: I slept (one night) in the house of Maimuna, the wife of the Apostle of Allah (may peace be upon him), and the Apostle of Allah (may peace be upon him) was with her that night. He (after sleeping for half of the night got up and) then performed ablution and then stood up and observed prayer. I too stood on his left side. He took hold of me and made me stand on his right side. He (the Holy Prophet) observed thirteen rak’ahs on that night. The Messenger of Allah (may peace be upon him) then slept and snored and it was a habit with him to snore while sleeping. The Mu’adhdbin then came to him (to inform him about the prayer). He then went out and observed prayer without performing ablution. (‘Amr said: Bukair b. Ashajj had narrated it to me )