Sahih al-Bukhari, Book 81, Hadith 51 (In-Book) ⓘ
Narrated `Aisha: The most beloved action to Allah's Messenger was that whose doer did it continuously and regularly.
حَدَّثَنَا قُتَيْبَةُ، عَنْ مَالِكٍ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ، أَنَّهَا قَالَتْ كَانَ أَحَبُّ الْعَمَلِ إِلَى رَسُولِ اللَّهِ صلى الله عليه وسلم الَّذِي يَدُومُ عَلَيْهِ صَاحِبُهُ.
also referenced under: Hadith 6462 (DarusSalam) & Volume 8, Book 76, Hadith 469 (USC-MSA)