Sahih al-Bukhari 1132
Sahih al-Bukhari · Book 19: Prayer at Night (Tahajjud) · Sleeping in the last hours of the night
Narrated Masruq:
حَدَّثَنِي عَبْدَانُ ، قَالَ أَخْبَرَنِي أَبِي ، عَنْ شُعْبَةَ ، عَنْ أَشْعَثَ ، 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. قُلْتُ مَتَى كَانَ يَقُومُ قَالَتْ يَقُومُ إِذَا سَمِعَ الصَّارِخَ.
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."