Yahya related to me from Malik from Ibn Shihab from Urwa ibn az- Zubayr that A'isha, the wife of the Prophet ﷺ said, "I never once saw the Messenger of Allah ﷺ doing the voluntary prayer of duha, but I myself do it. Sometimes the Messenger of Allah ﷺ would refrain from a practice that he loved to do, fearing that people would do the same and it would become fard for them ."
عَنْ عَائِشَةَ زَوْجِ النَّبِيِّ ﷺ أَنَّهَا قَالَتْ مَا رَأَيْتُ رَسُولَ اللَّهِ ﷺ يُصَلِّي سُبْحَةَ الضُّحَى قَطُّ وَإِنِّي لأُسَبِّحُهَا وَإِنْ كَانَ رَسُولُ اللَّهِ ﷺ لَيَدَعُ الْعَمَلَ وَهُوَ يُحِبُّ أَنْ يَعْمَلَهُ خَشْيَةَ أَنْ يَعْمَلَ بِهِ النَّاسُ فَيُفْرَضَ عَلَيْهِمْ