Jami` at-Tirmidhi 3146

Narrated Sa'eed bin Jubair:from Ibn 'Abbas regarding Allah's saying: "And offer your Salat neither aloud nor in a low voice but follow a way between." He said: "It was revealed when the Messenger of Allah (ﷺ) was hiding himself in Makkah, and when he led his Companions in Salat, he would raise his voice with the Qur'an. So when the idolaters heard it they would insult the Qur'an, the One Who revealed it, and the one who came with it. So Allah, Most High, said to His Prophet: 'And offer your Salat neither aloud' that is: Your recitation, so that the idolaters would not hear it and insult the Qur'an. 'Nor in a low voice (too low)' for your Companions, 'but follow a way between