Language:
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 6461

Narrated Masruq:

I asked `Aisha "What deed was the most beloved to the Prophet?" She said, "The regular constant one." I said, "At what time did he use to get up at night (for the Tahajjud night prayer)?' She said, "He used to get up on hearing (the crowing of) the cock (the last third of the night).

حَدَّثَنَا عَبْدَانُ، أَخْبَرَنَا أَبِي، عَنْ شُعْبَةَ، عَنْ أَشْعَثَ، قَالَ سَمِعْتُ أَبِي قَالَ، سَمِعْتُ مَسْرُوقًا، قَالَ سَأَلْتُ عَائِشَةَ ـ رضى الله عنها ـ أَىُّ الْعَمَلِ كَانَ أَحَبَّ إِلَى النَّبِيِّ صلى الله عليه وسلم قَالَتِ الدَّائِمُ‏.‏ قَالَ قُلْتُ فَأَىَّ حِينٍ كَانَ يَقُومُ قَالَتْ كَانَ يَقُومُ إِذَا سَمِعَ الصَّارِخَ‏.‏
Reference : Sahih al-Bukhari 6461
In-book reference : Book 81, Hadith 50
USC-MSA web (English) reference : Vol. 8, Book 76, Hadith 468
  (deprecated numbering scheme)