Narrated Sa'eed bin Jubair:
from Ibn 'Abbas, regarding: 'And offer your Salat neither aloud nor in a low voice (17:110)." He said: "It was revealed in Makkah. When the Messenger of Allah (ﷺ) would raise his voice with the Qur'an, the idolaters would insult him, the One Who revealed it, and the one who came with it. So Allah revealed: And offer your Salat neither aloud so that they would not insult the Qur'an and the One who revealed it, and the one who came with it, nor in a low voice (too low) such that you can let your Companions hear it, and learn it from you."
English reference: Vol. 5, Book 44, Hadith 3145
Arabic reference: Book 47, Hadith 3438