It was narrated that Abu Hurairah said: "The Messenger of Allah (ﷺ) said: 'When one of you enters the mosque, he is in a state of prayer, so long as the prayer keeps him there, and the angels will send prayer upon anyone of you so long as he remains in the place where he prayed, saying: "O Allah, forgive him; O Allah, have mercy on him; O Allah, accept his repentance," so long as he does not commit Hadath nor disturb anyone.'"
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا أَبُو مُعَاوِيَةَ، عَنِ الأَعْمَشِ، عَنْ أَبِي صَالِحٍ، عَنْ أَبِي هُرَيْرَةَ، قَالَ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ " إِنَّ أَحَدَكُمْ إِذَا دَخَلَ الْمَسْجِدَ كَانَ فِي صَلاَةٍ مَا كَانَتِ الصَّلاَةُ تَحْبِسُهُ وَالْمَلاَئِكَةُ يُصَلُّونَ عَلَى أَحَدِكُمْ مَادَامَ فِي مَجْلِسِهِ الَّذِي صَلَّى فِيهِ يَقُولُونَ اللَّهُمَّ اغْفِرْ لَهُ اللَّهُمَّ ارْحَمْهُ اللَّهُمَّ تُبْ عَلَيْهِ مَا لَمْ يُحْدِثْ فِيهِ مَا لَمْ يُؤْذِ فِيهِ " .
sunnah.com