Sahih Bukhari Volume 6, Book 65, Hadith 4571

حَدَّثَنَا سَعِيدُ بْنُ أَبِي مَرْيَمَ، أَخْبَرَنَا مُحَمَّدُ بْنُ جَعْفَرٍ، قَالَ أَخْبَرَنِي شَرِيكُ بْنُ عَبْدِ اللَّهِ بْنِ أَبِي نَمِرٍ، عَنْ كُرَيْبٍ، عَنِ ابْنِ عَبَّاسٍ ـ رضى الله عنهما ـ قَالَ بِتُّ عِنْدَ خَالَتِي مَيْمُونَةَ، فَتَحَدَّثَ رَسُولُ اللَّهِ صلى الله عليه وسلم مَعَ أَهْلِهِ سَاعَةً ثُمَّ رَقَدَ، فَلَمَّا كَانَ ثُلُثُ اللَّيْلِ الآخِرُ قَعَدَ فَنَظَرَ إِلَى السَّمَاءِ فَقَالَ ‏{‏إِنَّ فِي خَلْقِ السَّمَوَاتِ وَالأَرْضِ وَاخْتِلاَفِ اللَّيْلِ وَالنَّهَارِ لآيَاتٍ لأُولِي الأَلْبَابِ‏}‏، ثُمَّ قَامَ فَتَوَضَّأَ وَاسْتَنَّ، فَصَلَّى إِحْدَى عَشْرَةَ رَكْعَةً، ثُمَّ أَذَّنَ بِلاَلٌ فَصَلَّى رَكْعَتَيْنِ، ثُمَّ خَرَجَ فَصَلَّى الصُّبْحَ‏.‏

Narrated By Ibn 'Abbas : I stayed overnight in the house of my aunt Maimuna. Allah's Apostle talked with his wife for a while and then went to bed. When it was the last third of the night, he got up and looked towards the sky and said: "Verily! In the creation of the Heavens and the Earth and in the alteration of night and day, there are indeed signs for men of understanding." (3.190) Then he stood up, performed ablution, brushed his teeth with a Siwak, and then prayed eleven Rakat. Then Bilal pronounced the Adhan (i.e. call for the Fajr prayer). The Prophet then offered two Rakat (Sunna) prayer and went out (to the Mosque) and offered the (compulsory congregational) Fajr prayer.