The Book of Prayer - Travellers
6/13. Chapter:
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
Sahih Muslim
وَحَدَّثَنَا يَحْيَى بْنُ يَحْيَى، أَخْبَرَنَا يَزِيدُ بْنُ زُرَيْعٍ، عَنْ سَعِيدٍ الْجُرَيْرِيِّ، عَنْ عَبْدِ اللَّهِ بْنِ شَقِيقٍ، قَالَ قُلْتُ لِعَائِشَةَ هَلْ كَانَ النَّبِيُّ صلى الله عليه وسلم يُصَلِّي الضُّحَى قَالَتْ لاَ إِلاَّ أَنْ يَجِيءَ مِنْ مَغِيبِهِ .
'Abdullah b. Shaqiq reported: I asked 'A'isha whether the Messenger of Allah (ﷺ) used to observe the forenoon prayer. She said: No, but when he came back from the journey.
Reference : Sahih Muslim 717aIn-book reference : Book 6, Hadith 90USC-MSA web (English) reference : Book 4, Hadith 1546