Narrated AbuSa'id al-Khudri: The Messenger of Allah (ﷺ) retired to the mosque. He heard them (the people) reciting the Qur'an in a loud voice. He removed the curtain and said: Lo! every one of you is calling his Lord quietly. One should not trouble the other and one should not raise the voice in recitation or in prayer over the voice of the other.
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا الْحَسَنُ بْنُ عَلِيٍّ، حَدَّثَنَا عَبْدُ الرَّزَّاقِ، أَخْبَرَنَا مَعْمَرٌ، عَنْ إِسْمَاعِيلَ بْنِ أُمَيَّةَ، عَنْ أَبِي سَلَمَةَ، عَنْ أَبِي سَعِيدٍ، قَالَ : اعْتَكَفَ رَسُولُ اللَّهِ صلى الله عليه وسلم فِي الْمَسْجِدِ فَسَمِعَهُمْ يَجْهَرُونَ بِالْقِرَاءَةِ، فَكَشَفَ السِّتْرَ وَقَالَ : " أَلاَ إِنَّ كُلَّكُمْ مُنَاجٍ رَبَّهُ فَلاَ يُؤْذِيَنَّ بَعْضُكُمْ بَعْضًا، وَلاَ يَرْفَعْ بَعْضُكُمْ عَلَى بَعْضٍ فِي الْقِرَاءَةِ " . أَوْ قَالَ : " فِي الصَّلاَةِ " .
sunnah.com