Narrated Ibn 'Abbas:

regarding the explanation of the Verse:-- '(O Muhammad!) 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 at Mecca. At that time, when he led his companions in prayer, he used to raise his voice while reciting the Qur'an;
and if the pagans heard him, they would abuse the Qur'an, its Revealer, and the one who brought it. So Allah said to His Prophet: "Neither say your prayer aloud. i.e., your recitation (of Qur'an) lest the pagans should hear (it) and abuse the Quran" nor say it in a low tone, "lest your voice should fail to reach your companions, "but follow a way between." (17.110)

حَدَّثَنِي عَمْرُو بْنُ زُرَارَةَ، عَنْ هُشَيْمٍ، أَخْبَرَنَا 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 ﷺ مُخْتَفٍ بِمَكَّةَ، فَكَانَ إِذَا صَلَّى بِأَصْحَابِهِ رَفَعَ صَوْتَهُ بِالْقُرْآنِ، فَإِذَا سَمِعَهُ الْمُشْرِكُونَ سَبُّوا الْقُرْآنَ وَمَنْ أَنْزَلَهُ وَمَنْ جَاءَ بِهِ، فَقَالَ اللَّهُ لِنَبِيِّهِ ﷺ {وَلاَ تَجْهَرْ بِصَلاَتِكَ} أَىْ بِقِرَاءَتِكَ، فَيَسْمَعَ الْمُشْرِكُونَ، فَيَسُبُّوا الْقُرْآنَ {وَلاَ تُخَافِتْ بِهَا} عَنْ أَصْحَابِكَ فَلاَ تُسْمِعُهُمْ {وَابْتَغِ بَيْنَ ذَلِكَ سَبِيلاً}