Muwatta Malik · 422

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ، زَوْجِ النَّبِيِّ صلى الله عليه وسلم أَنَّهَا قَالَتْ كَانَ أَحَبُّ الْعَمَلِ إِلَى رَسُولِ اللَّهِ صلى الله عليه وسلم الَّذِي يَدُومُ عَلَيْهِ صَاحِبُهُ ‏.‏

Yahya related to me from Malik from Hisham ibn Urwa from his father that A'isha, the wife of the Prophet, may Allah bless him and grant him peace, said, "The actions which the Messenger of Allah, may Allah bless him and grant him peace, loved most were those which were done most constantly