Translation
(81) To make the Heart Tender (Ar-Riqaq)
كتاب الرقاق
(18) Chapter: The adoption of a middle course, and the regularity of deeds
(18) باب الْقَصْدِ وَالْمُدَاوَمَةِ عَلَى الْعَمَلِ
Sahih al-Bukhari 6465 

Narrated `Aisha:

The Prophet (ﷺ) was asked, "What deeds are loved most by Allah?" He said, "The most regular constant deeds even though they may be few." He added, 'Don't take upon yourselves, except the deeds which are within your ability."

حَدَّثَنِي مُحَمَّدُ بْنُ عَرْعَرَةَ، حَدَّثَنَا شُعْبَةُ، عَنْ سَعْدِ بْنِ إِبْرَاهِيمَ، عَنْ أَبِي سَلَمَةَ، عَنْ عَائِشَةَ ـ رضى الله عنها ـ أَنَّهَا قَالَتْ سُئِلَ النَّبِيُّ صلى الله عليه وسلم أَىُّ الأَعْمَالِ أَحَبُّ إِلَى اللَّهِ قَالَ ‏"‏ أَدْوَمُهَا وَإِنْ قَلَّ ‏"‏‏.‏ وَقَالَ ‏"‏ اكْلَفُوا مِنَ الأَعْمَالِ مَا تُطِيقُونَ ‏"‏‏.‏
Reference : Sahih al-Bukhari 6465
In-book reference : Book 81, Hadith 54
USC-MSA web (English) reference : Vol. 8, Book 76, Hadith 472
  (deprecated numbering scheme)