Sahih al-Bukhari 3229
Sahih al-Bukhari · Book 59: Beginning of Creation · If anyone says Amin [during the Salat (prayer) at the end of the recitation of Surat Al-Fatiha]
Narrated Abu Huraira:
حَدَّثَنَا إِبْرَاهِيمُ بْنُ الْمُنْذِرِ ، حَدَّثَنَا مُحَمَّدُ بْنُ فُلَيْحٍ ، حَدَّثَنَا أَبِي ، عَنْ هِلاَلِ بْنِ عَلِيٍّ ، عَنْ عَبْدِ الرَّحْمَنِ بْنِ أَبِي عَمْرَةَ ، عَنْ أَبِي هُرَيْرَةَ ـ رضى الله عنه ـ عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " إِنَّ أَحَدَكُمْ فِي صَلاَةٍ مَا دَامَتِ الصَّلاَةُ تَحْبِسُهُ، وَالْمَلاَئِكَةُ تَقُولُ اللَّهُمَّ اغْفِرْ لَهُ وَارْحَمْهُ. مَا لَمْ يَقُمْ مِنْ صَلاَتِهِ أَوْ يُحْدِثْ " .
The Prophet (ﷺ) said, "As long as any-one of you is waiting for the prayer, he is considered to be praying actually, and the angels say, 'O Allah! Be merciful to him and forgive him', (and go on saying so) unless he leaves his place of praying or passes wind (i.e. breaks his ablution).