Sahih Muslim Book 004, Hadith Number 1677.
Chapter : Encouragement to observe prayers during Ramadhan and that is Tarawih.
Ibn 'Abbas said: I spent the night in the house of my mother's sister, Maimuna, and observed how the Messenger of Allah (may peace be upon him) prayed (at night). He got up and relieved himself. He then washed his face and hands and then went to sleep. He again got up and went near the water-skin and loosened its straps and then poured some water in a bowl and inclined it with his hands (towards himself). He then performed a good ablution between the two extremes and then stood up to pray. I also came and stood by his left side. He took hold of me and made me stand on his right side. It was in thirteen rak'ahs that the (night) prayer of the Messenger of Allah (may peace be upon him) was completed. He then slept till he began to snore, and we knew that he had gone to sleep by his snoring. He then went out (for the dawn prayer) and then again slept, and said while praying or prostrating himself: "O Allah ! place light in my heart, light in my hearing, light in my sight, light on my right, light on my left, light in front of me, light behind me, light above me, light below me, make light for me," or he said: "Make me light."