Prayer at Night (Tahajjud)

Bukhari :: Book 2 :: Volume 21 :: Hadith 232

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."