Sahih Bukhari Volume 6, Book 65, Hadith 4724

حَدَّثَنَا يَعْقُوبُ بْنُ إِبْرَاهِيمَ، حَدَّثَنَا هُشَيْمٌ، حَدَّثَنَا أَبُو بِشْرٍ، عَنْ سَعِيدِ بْنِ جُبَيْرٍ، عَنِ ابْنِ عَبَّاسٍ ـ رضى الله عنهما ـ فِي قَوْلِهِ تَعَالَى ‏{‏وَلاَ تَجْهَرْ بِصَلاَتِكَ وَلاَ تُخَافِتْ بِهَا‏}‏ قَالَ نَزَلَتْ وَرَسُولُ اللَّهِ صلى الله عليه وسلم مُخْتَفٍ بِمَكَّةَ، كَانَ إِذَا صَلَّى بِأَصْحَابِهِ رَفَعَ صَوْتَهُ بِالْقُرْآنِ فَإِذَا سَمِعَهُ الْمُشْرِكُونَ سَبُّوا الْقُرْآنَ وَمَنْ أَنْزَلَهُ، وَمَنْ جَاءَ بِهِ، فَقَالَ اللَّهُ تَعَالَى لِنَبِيِّهِ صلى الله عليه وسلم ‏{‏وَلاَ تَجْهَرْ بِصَلاَتِكَ‏}‏ أَىْ بِقِرَاءَتِكَ، فَيَسْمَعَ الْمُشْرِكُونَ، فَيَسُبُّوا الْقُرْآنَ، ‏{‏وَلاَ تُخَافِتْ بِهَا‏}‏ عَنْ أَصْحَابِكَ فَلاَ تُسْمِعُهُمْ ‏{‏وَابْتَغِ بَيْنَ ذَلِكَ سَبِيلاً‏}‏‏.

Narrated By Ibn Abbas : (Regarding): 'Neither say your, prayer aloud, nor say it in a low tone.' (17.110) This Verse was revealed while Allah's Apostle was hiding himself in Mecca. When he prayed with his companions, he used to raise his voice with the recitation of Qur'an, and if the pagans happened to hear him, they would abuse the Qur'an, the One who revealed it and the one who brought it. Therefore Allah said to His Prophet : 'Neither say your prayer aloud.' (17.110) i.e. do not recite aloud lest the pagans should hear you, but follow a way between.