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كتاب الرقاق
81  
To make the Heart Tender (Ar-Riqaq)
(18)
Chapter: The adoption of a middle course, and the regularity of deeds
(18)
باب الْقَصْدِ وَالْمُدَاوَمَةِ عَلَى الْعَمَلِ
Sahih al-Bukhari 6462

Narrated `Aisha:

The most beloved action to Allah's Messenger (ﷺ) 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.‏
Reference : Sahih al-Bukhari 6462
In-book reference : Book 81, Hadith 51
USC-MSA web (English) reference : Vol. 8, Book 76, Hadith 469
  (deprecated numbering scheme)