Narrated 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.
• Sahih al-Bukhari, Vol. 6, Book of Prophetic Commentary on the Qur'an, Hadith 246
• Sahih al-Bukhari, Book of Prophetic Commentary on the Qur'an, Hadith 246