Surah Al-Isra' (The Night Journey), Verse 110

قُلِ ادْعُوا اللّٰهَ اَوِ ادْعُوا الرَّحْمٰنَ اَیًّا مَّا تَدْعُوْا فَلَهُ الْاَسْمَآءُ الْحُسْنٰی وَلَا تَجْهَرْ بِصَلَاتِكَ وَلَا تُخَافِتْ بِهَا وَابْتَغِ بَیْنَ ذٰلِكَ سَبِیْلًا ۟

Qulid'ul laaha awid'ur Rahmaana ayyam maa tad'oo falahul asmaaa'ul Husnaa; wa laa tajhar bi Salaatika wa laa tukhaafit bihaa wabtaghi baina zaalika sabeela

“Say: "Call upon Allah, or call upon Rahman: by whatever name ye call upon Him, (it is well): for to Him belong the Most Beautiful Names. Neither speak thy Prayer aloud, nor speak it in a low tone, but seek a middle course between."”

Quran 17:110 (Yusuf Ali Translation)