Musnad Ahmad 1852
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated that Ibn "Abbas said: This verse was revealed when the Messenger of Allah (ﷺ) was preaching in secret in Makkah: And offer your salah (prayer) aloud nor in la low voice. [al-Isra" 17:110]. When the Prophet (ﷺ) led his Companions in prayer, he would raise his voice when reciting the Qur"an, and whenever the mushrikeen heard that, they would revile the Qur"an, and they would revile the One Who revealed it and the one who brought it. So Allah, may He be glorified and exalted, said to His Prophet (ﷺ) "And offer your Salah (prayer) neither aloud", i.e., lest the mushrikeen hear you and revile the Qur"an, "nor in a low voice", i.e., so low that your Companions cannot hear the Qur"an and learn it from you. “But follow a way between"[al-Isra" 17:110].