Sahih al-Bukhari, Volume 8, Book 76, Hadith 469 (USC-MSA) ⓘ
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: Book 81, Hadith 51 (In-Book) & Hadith 6462 (DarusSalam)