Mishkat al-Masabih 4 Prayer كتاب الصلاة 623

عَنْ مَسْرُوقٍ قَالَ: سَأَلْتُ عَائِشَةَ: أَيُّ الْعَمَلِ كَانَ أَحَبَّ إِلَى رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ؟ قَالَتْ: الدَّائِمُ قُلْتُ: فَأَيُّ حِينَ كَانَ يَقُومُ مِنَ اللَّيْلِ؟ قَالَتْ: كَانَ يَقُومُ إِذا سمع الصَّارِخ

Masruq said he asked ‘A’isha what action was most pleasing to God’s Messenger and she replied that it was what one keeps on doing. He asked at what time he got up at night and she said it was at cockcrow. (Bukhari and Muslim.)