(13) باب اسْتِحْبَابِ صَلاَةِ الضُّحَى وَأَنَّ أَقَلَّهَا رَكْعَتَانِ وَأَكْمَلَهَا ثَمَانِ رَكَعَاتٍ وَأَوْسَطَهَا أَرْبَعُ رَكَعَاتٍ أَوْ سِتٌّ وَالْحَثِّ عَلَى الْمُحَافَظَةِ عَلَيْهَا
Abu Murra, the freed slave of Umm Hani, daughter of Abu Talib, reported Umm Hani to be saying:
I went to the Messenger of Allah (ﷺ) on the day of the Conquest of Mecca and found him taking a bath, and Fatimah, his daughter, had provided him privacy with the help of a cloth. I gave him salutation and he said: Who is she? I said: It is Umm Hani, daughter of Abu Talib. He (the Holy Prophet) said: Greeting for Umm Hani. When he had completed the bath, he stood up and observed eight rak'ahs wrapped up in one cloth. When he turned back (after the prayer), I said to him: Messenger of Allah, the son of my mother 'Ali b. Abu Talib is going to kill a person, Fulan b. Hubaira whom I have given protection. Upon this the Messenger of Allah (ﷺ) said: We too have given protection whom you have given protection, O Umm Hani. Umm Hani said: It was the forenoon (prayer).
Reference: Sahih Muslim 336 f
In-book reference: Book 6, Hadith 99
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 1555