Sunan an-Nasa'i, Book 11, Hadith 137 (In-Book) ⓘ

It was narrated that Ibn Abbas said: "The Prophet used to raise his voice when reciting Quran, and when the idolaters heard his voice they would insult the Quran and the one who had brought it. So the Prophet began to lower his voice such that his companions would not hear him. Then Allah (SWT), the Mighty and Sublime, revealed: 'And offer your salah (prayer) neither aloud nor in a low voice, but follow a way between.'"

أَخْبَرَنَا مُحَمَّدُ بْنُ قُدَامَةَ، قَالَ حَدَّثَنَا جَرِيرٌ، عَنِ الأَعْمَشِ، عَنْ جَعْفَرِ بْنِ إِيَاسٍ، عَنْ سَعِيدِ بْنِ جُبَيْرٍ، عَنِ ابْنِ عَبَّاسٍ، قَالَ كَانَ النَّبِيُّ صلى الله عليه وسلم يَرْفَعُ صَوْتَهُ بِالْقُرْآنِ وَكَانَ الْمُشْرِكُونَ إِذَا سَمِعُوا صَوْتَهُ سَبُّوا الْقُرْآنَ وَمَنْ جَاءَ بِهِ فَكَانَ النَّبِيُّ صلى الله عليه وسلم يَخْفِضُ صَوْتَهُ بِالْقُرْآنِ مَا كَانَ يَسْمَعُهُ أَصْحَابُهُ فَأَنْزَلَ اللَّهُ عَزَّ وَجَلَّ ‏{‏ وَلاَ تَجْهَرْ بِصَلاَتِكَ وَلاَ تُخَافِتْ بِهَا وَابْتَغِ بَيْنَ ذَلِكَ سَبِيلاً ‏}‏ ‏"‏ ‏.‏