(13) باب اسْتِحْبَابِ صَلاَةِ الضُّحَى وَأَنَّ أَقَلَّهَا رَكْعَتَانِ وَأَكْمَلَهَا ثَمَانِ رَكَعَاتٍ وَأَوْسَطَهَا أَرْبَعُ رَكَعَاتٍ أَوْ سِتٌّ وَالْحَثِّ عَلَى الْمُحَافَظَةِ عَلَيْهَا
Abd al-Rahman b. Abu Laila reported:
No one has ever narrated to me that he saw the Messenger of Allah (ﷺ) observing the forenoon prayer, except Umm Hani. She, however, narrated that the Messenger of Allah (ﷺ) entered her house on the day of the Conquest of Mecca and prayed eight rak'ahs (adding): I never saw a shorter prayer than it except that he performed the bowing and prostration completely. But (one of the narrators) Ibn Bashshar in his narration made no mention of the word:" Never".
Reference: Sahih Muslim 336 d
In-book reference: Book 6, Hadith 97
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 1553