Sahih al-Bukhari, Book 64, Hadith 325 (In-Book) ⓘ

Narrated Ibn Abi Laila: None informed us that he saw the Prophet offering the Duha (i.e. forenoon) prayer, except Um Hani who mentioned that the Prophet took a bath in her house on the day of the Conquest (of Mecca) and then offered an eight rak`at prayer. She added, "I never saw the Prophet offering a lighter prayer than that prayer, but he was performing perfect bowing and prostrations."

حَدَّثَنَا أَبُو الْوَلِيدِ، حَدَّثَنَا شُعْبَةُ، عَنْ عَمْرٍو، عَنِ ابْنِ أَبِي لَيْلَى، مَا أَخْبَرَنَا أَحَدٌ، أَنَّهُ رَأَى النَّبِيَّ صلى الله عليه وسلم يُصَلِّي الضُّحَى غَيْرَ أُمِّ هَانِئٍ، فَإِنَّهَا ذَكَرَتْ أَنَّهُ يَوْمَ فَتْحِ مَكَّةَ اغْتَسَلَ فِي بَيْتِهَا ثُمَّ صَلَّى ثَمَانِيَ رَكَعَاتٍ، قَالَتْ لَمْ أَرَهُ صَلَّى صَلاَةً أَخَفَّ مِنْهَا غَيْرَ أَنَّهُ يُتِمُّ الرُّكُوعَ وَالسُّجُودَ‏.‏