Abdullah bin Abbas reported,

Concerning the words of Allah , "And do not raise your voice in your prayer, nor be too quiet in it" [Isra 17:110], he said, This was revealed while the Messenger of Allah ﷺ was in hiding at Makkah. Whenever he led his companions in prayer, he would raise his voice with the Quran, and when the idolaters heard it they would insult the Quran, the One who sent it down, and the one who brought it. So Allah Almighty said to His Prophet ﷺ, "And do not raise your voice in your prayer" so that the idolaters hear your recitation, "nor be too quiet in it" so that your companions cannot hear. Let them hear the Quran, but do not raise your voice that loudly. "But seek between that a way", meaning between raising the voice and lowering it.

حدثنا أبو جعفر محمد بن الصباح وعمرو الناقد جميعا عن هشيم قال ابن الصباح حدثنا هشيم أخبرنا أبو بشر عن سعيد بن جبير

عن ابن عباس

في قوله عز وجل {ولا تجهر بصلاتك ولا تخافت بها} قال نزلت ورسول الله ﷺ متوار بمكة فكان إذا صلى بأصحابه رفع صوته بالقرآن فإذا سمع ذلك المشركون سبوا القرآن ومن أنزله ومن جاء به فقال الله تعالى لنبيه ﷺ {ولا تجهر بصلاتك} فيسمع المشركون قراءتك {ولا تخافت بها} عن أصحابك أسمعهم القرآن ولا تجهر ذلك الجهر {وابتغ بين ذلك سبيلا} يقول بين الجهر والمخافتة