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 إِسْحَاقُ بْنُ إِبْرَاهِيمَ، وَابْنُ، بَشَّارٍ جَمِيعًا عَنْ مُعَاذِ بْنِ هِشَامٍ، قَالَ حَدَّثَنِي أَبِي، عَنْ قَتَادَةَ، بِهَذَا الإِسْنَادِ مِثْلَهُ .
A hadith like this has been narrated by Qatada with the same chain of transmitters.
Reference : Sahih Muslim 719dIn-book reference : Book 6, Hadith 96USC-MSA web (English) reference : Book 4, Hadith 1552