(13) باب اسْتِحْبَابِ صَلاَةِ الضُّحَى وَأَنَّ أَقَلَّهَا رَكْعَتَانِ وَأَكْمَلَهَا ثَمَانِ رَكَعَاتٍ وَأَوْسَطَهَا أَرْبَعُ رَكَعَاتٍ أَوْ سِتٌّ وَالْحَثِّ عَلَى الْمُحَافَظَةِ عَلَيْهَا
'Urwa reported 'A'isha to be sayidg:
I have never seen the Messenger of Allah (ﷺ) observing the supererogatory prayer of the forenoon, but I observed it. And if the Messenger of Allah (ﷺ) abandoned any act which he in fact loved to do, it was out of fear that if the people practised it constantly, it might become obligatory for them.
Reference: Sahih Muslim 718
In-book reference: Book 6, Hadith 92
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 1548