Sahih Bukhari Volume 9, Book 93, Hadith Number 544.

Narrated By Ibn ‘Abbas : Once I stayed overnight at the house of (my aunt) Maimuna while the Prophet was with her, to see how was the night prayer of Allah s Apostle Allah’s Apostle talked to his wife for a while and then slept. When it was the last third of the night (or part of it), the Prophet got up and looked towards the sky and recited the Verse: ‘Verily! In the creation of the Heavens and the Earth… there are indeed signs for the men of understanding.’ (3.190)

Then He got up and performed the ablution, brushed his teeth and offered eleven Rakat. Then Bilal pronounced the Adhan whereupon the Prophet offered a two-Rak’at (Sunna) prayer and went out to lead the people in Fajr (morning compulsory congregational prayer.