Sahih Bukhari Volume 9, Book 97, Hadith 7431

حَدَّثَنَا إِسْمَاعِيلُ، حَدَّثَنِي مَالِكٌ، عَنْ أَبِي الزِّنَادِ، عَنِ الأَعْرَجِ، عَنْ أَبِي هُرَيْرَةَ ـ رضى الله عنه ـ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏"‏ يَتَعَاقَبُونَ فِيكُمْ مَلاَئِكَةٌ بِاللَّيْلِ وَمَلاَئِكَةٌ بِالنَّهَارِ، وَيَجْتَمِعُونَ فِي صَلاَةِ الْعَصْرِ وَصَلاَةِ الْفَجْرِ، ثُمَّ يَعْرُجُ الَّذِينَ بَاتُوا فِيكُمْ فَيَسْأَلُهُمْ وَهْوَ أَعْلَمُ بِكُمْ فَيَقُولُ كَيْفَ تَرَكْتُمْ عِبَادِي فَيَقُولُونَ تَرَكْنَاهُمْ وَهُمْ يُصَلُّونَ وَأَتَيْنَاهُمْ وَهُمْ يُصَلُّونَ ‏"‏‏

Narrated By Abu Huraira : Allah's Apostle said, "(A group of) angels stay with you at night and (another group of) angels by daytime, and both groups gather at the time of the 'Asr and Fajr prayers. Then those angels who have stayed with you overnight, ascend (to Heaven) and Allah asks them (about you)... and He knows everything about you. "In what state did you leave My slaves?' The angels reply, 'When we left them, they were praying, and when we reached them they were praying.'"