(18) باب الْقَصْدِ وَالْمُدَاوَمَةِ عَلَى الْعَمَلِ
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).
Reference: Sahih al-Bukhari 6461
In-book reference: Book 81, Hadith 50
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 8, Book 76, Hadith 468