Language:
كتاب الأذان
10  
Call to Prayers (Adhaan)
(36)
Chapter: (The reward of a person) who waits for As-Salat (the prayer) in the mosque and the superiority of mosques
(36)
باب مَنْ جَلَسَ فِي الْمَسْجِدِ يَنْتَظِرُ الصَّلاَةَ، وَفَضْلِ الْمَسَاجِدِ
Sahih al-Bukhari 659

Narrated Abu Huraira:

Allah's Messenger (ﷺ) said, "The angels keep on asking for Allah's Blessing and Forgiveness for anyone of you as long as he is at his Musalla (praying place) and does not do Hadath (passes wind). The angels say, 'O Allah! Forgive him and be Merciful to him.' Each one of you is in the prayer as long as he is waiting for the prayer and nothing but the prayer detains him from going to his family."

حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ، عَنْ مَالِكٍ، عَنْ أَبِي الزِّنَادِ، عَنِ الأَعْرَجِ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏ "‏ الْمَلاَئِكَةُ تُصَلِّي عَلَى أَحَدِكُمْ مَا دَامَ فِي مُصَلاَّهُ مَا لَمْ يُحْدِثْ اللَّهُمَّ اغْفِرْ لَهُ، اللَّهُمَّ ارْحَمْهُ‏.‏ لاَ يَزَالُ أَحَدُكُمْ فِي صَلاَةٍ مَا دَامَتِ الصَّلاَةُ تَحْبِسُهُ، لاَ يَمْنَعُهُ أَنْ يَنْقَلِبَ إِلَى أَهْلِهِ إِلاَّ الصَّلاَةُ ‏"‏‏.‏
Reference : Sahih al-Bukhari 659
In-book reference : Book 10, Hadith 53
USC-MSA web (English) reference : Vol. 1, Book 11, Hadith 628
  (deprecated numbering scheme)