Sahih Bukhari Volume 9, Book 97, Hadith 7488

حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، عَنْ مَالِكٍ، عَنْ أَبِي الزِّنَادِ، عَنِ الأَعْرَجِ، عَنْ أَبِي هُرَيْرَةَ، 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 كَيْفَ تَرَكْتُمْ عِبَادِي فَيَقُولُونَ تَرَكْنَاهُمْ وَهُمْ يُصَلُّونَ، وَأَتَيْنَاهُمْ وَهُمْ يُصَلُّونَ ‏"

Narrated By Abu Huraira : Allah's Apostle said, "There are angels coming to you in succession at night, and others during the day, and they all gather at the time of 'Asr and Fajr prayers. Then the angels who have stayed with you overnight ascend (to the heaven) and He (Allah) asks them though He perfectly knows their affairs. 'In what state have you left my slaves?' They say, 'When we left them, they were praying and when we came to them they were praying.'"