Sahih Bukhari Volume 2, Book 19, Hadith 1177

حَدَّثَنَا آدَمُ، حَدَّثَنَا شُعْبَةُ، حَدَّثَنَا عَمْرُو بْنُ مُرَّةَ، قَالَ سَمِعْتُ عَبْدَ الرَّحْمَنِ بْنَ أَبِي لَيْلَى، يَقُولُ مَا حَدَّثَنَا أَحَدٌ، أَنَّهُ رَأَى النَّبِيَّ صلى الله عليه وسلم يُصَلِّي الضُّحَى غَيْرَ أُمِّ هَانِئٍ فَإِنَّهَا قَالَتْ إِنَّ النَّبِيَّ صلى الله عليه وسلم دَخَلَ بَيْتَهَا يَوْمَ فَتْحِ مَكَّةَ فَاغْتَسَلَ وَصَلَّى ثَمَانِيَ رَكَعَاتٍ فَلَمْ أَرَ صَلاَةً قَطُّ أَخَفَّ مِنْهَا، غَيْرَ أَنَّهُ يُتِمُّ الرُّكُوعَ وَالسُّجُودَ‏

Narrated By 'Abdur Rahman bin Abi Laila : Only Um Hani narrated to me that she had seen the Prophet offering the Duha prayer. She said, "On the day of the conquest of Mecca, the Prophet entered my house, took a bath and offered eight Rakat (of Duha prayers. I had never seen the Prophet offering such a light prayer but he performed bowing and prostrations perfectly.