Sahih al-Bukhari 6461

Arabic

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.‏

English translation

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, Book of To make the Heart Tender (Ar-Riqaq). English translation by Dr. Muhammad Muhsin Khan.