Sahih Muslim 336
Sahih Muslim · Book 6: The Book of Prayer - Travellers · It is recommended to pray Duha, the least of which is two rak`ah, the best of which is eight, and the average of which is four or six, and encouragement to do so regularly
وَحَدَّثَنِي حَجَّاجُ بْنُ الشَّاعِرِ ، حَدَّثَنَا مُعَلَّى بْنُ أَسَدٍ ، حَدَّثَنَا وُهَيْبُ بْنُ خَالِدٍ ، عَنْ جَعْفَرِ بْنِ مُحَمَّدٍ ، عَنْ أَبِيهِ ، عَنْ أَبِي مُرَّةَ ، مَوْلَى عَقِيلٍ عَنْ أُمِّ هَانِئٍ ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم صَلَّى فِي بَيْتِهَا عَامَ الْفَتْحِ ثَمَانِيَ رَكَعَاتٍ فِي ثَوْبٍ وَاحِدٍ قَدْ خَالَفَ بَيْنَ طَرَفَيْهِ .
Abu Murra narrated on the authority of Umm Hani that the Messenger of Allah (ﷺ) on the day of the Conquest of Mecca observed in her house eight rak'ahs of prayer in one cloth, its opposite corners having been tied from the opposite sides.