Sahih al-Bukhari 59:39
Narrated Abu Huraira:
Allah's Messenger (ﷺ) said, "When the Imam, during the prayer, says, "Allah hears him who praises Him', say: 'O Allah! Our Lord! All the praises are for You/, for if the saying of anyone of you coincides with the saying of the angels, his past sins will be forgiven."
Reference
Sahih al-Bukhari 59:39
In-book reference
Book 59, Hadith 39
Arabic Text
حَدَّثَنَا إِسْمَاعِيلُ، قَالَ حَدَّثَنِي مَالِكٌ، عَنْ سُمَىٍّ، عَنْ أَبِي صَالِحٍ، عَنْ أَبِي هُرَيْرَةَ ـ رضى الله عنه ـ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " إِذَا قَالَ الإِمَامُ سَمِعَ اللَّهُ لِمَنْ حَمِدَهُ. فَقُولُوا اللَّهُمَّ رَبَّنَا لَكَ الْحَمْدُ، فَإِنَّهُ مَنْ وَافَقَ قَوْلُهُ قَوْلَ الْمَلاَئِكَةِ، غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ ".