Sahih Al Bukhari Hadith Number 1132

Narrated Masruq: I asked `Aisha which deed was most loved by the Prophet. She said, “A deed done continuously.” I further asked, “When did he used to get up (in the night for the prayer).” She said, “He used to get up on hearing the crowing of a cock.”

19  Prayer at Night (Tahajjud)
Hadith number 1132
Volume no 2
Chapter: 7 (Sleeping in the last hours of the night)