From Sahih Bukhari (Hadith 1128):
Narrated `Aisha:Allah's Messenger (ﷺ) used to give up a good deed, although he loved to do it, for fear that people might act on it and it might be made compulsory for them. The Prophet (ﷺ) never prayed the Duha prayer, but I offer it
Reference: Bukhari 1128