Sahih Al Bukhari Hadith Number 1128

Narrated `Aisha: Allah’s Messenger (peace be upon him) 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 (peace eb upon him) never prayed the Duha prayer, but I offer it.

19  Prayer at Night (Tahajjud)
Hadith number 1128
Volume no 2
Chapter: 5 ( The Prophet’s (peace eb upon him) exhorting to Tahajjud and Nawafil without making them compulsory)