The word of (Allah) Great and Glorious: 'And utter not thy prayer loudly, nor be low in it" (xvii. 110) was revealed as the Messenger of Allah (may peace beupon him) was hiding himself in Mecca. When he led his Companions in prayer he raised his voice (while reciting the) Qur'an. And when the polytheists heard that, they reviled the Qur'an and Him Who revealed it and him who brought it. Upon this Allah, the Exalted, said to His Apostle ﷺ: Utter not thy prayer so loudly that the polytheists may hear thy recitation and (recite it) not so low that it may be inaudible to your Companions. Make them hear the Qur'an, but do not recite it loudly and seek a (middle) way between these. Recite between loud and low tone.  

فِي قَوْلِهِ ﷻ { وَلاَ تَجْهَرْ بِصَلاَتِكَ وَلاَ تُخَافِتْ بِهَا} قَالَ نَزَلَتْ وَرَسُولُ اللَّهِ ﷺ مُتَوَارٍ بِمَكَّةَ فَكَانَ إِذَا صَلَّى بِأَصْحَابِهِ رَفَعَ صَوْتَهُ بِالْقُرْآنِ فَإِذَا سَمِعَ ذَلِكَ الْمُشْرِكُونَ سَبُّوا الْقُرْآنَ وَمَنْ أَنْزَلَهُ وَمَنْ جَاءَ بِهِ فَقَالَ اللَّهُ تَعَالَى لِنَبِيِّهِ ﷺ { وَلاَ تَجْهَرْ بِصَلاَتِكَ} فَيَسْمَعَ الْمُشْرِكُونَ قِرَاءَتَكَ { وَلاَ تُخَافِتْ بِهَا} عَنْ أَصْحَابِكَ أَسْمِعْهُمُ الْقُرْآنَ وَلاَ تَجْهَرْ ذَلِكَ الْجَهْرَ وَابْتَغِ بَيْنَ ذَلِكَ سَبِيلاً يَقُولُ بَيْنَ الْجَهْرِ وَالْمُخَافَتَةِ  

" And utter not thy prayer loudly, not be low in it" (xvii. 110) relate to supplication (du'a').  

عَنْ عَائِشَةَ فِي قَوْلِهِ ﷻ { وَلاَ تَجْهَرْ بِصَلاَتِكَ وَلاَ تُخَافِتْ بِهَا} قَالَتْ أُنْزِلَ هَذَا فِي الدُّعَاءِ  

A hadith like this has been narrated by Hisham with the same chain of transmitters.  

عَنْ هِشَامٍ بِهَذَا الإِسْنَادِ مِثْلَهُ