Al-Isra' - 17:110

قُلِ ادْعُواْ اللّهَ أَوِ ادْعُواْ الرَّحْمَـنَ أَيًّا مَّا تَدْعُواْ فَلَهُ الأَسْمَاء الْحُسْنَى وَلاَ تَجْهَرْ بِصَلاَتِكَ وَلاَ تُخَافِتْ بِهَا وَابْتَغِ بَيْنَ ذَلِكَ سَبِيلاً
[17:110]
Say: Call upon Allah or call upon, the Beneficent Allah; whichever you call upon, He has the best names; and do not utter your prayer with a very raised voice nor be silent with regard to it, and seek a way between these.
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."
Say (unto mankind): Cry unto Allah, or cry unto the Beneficent, unto whichsoever ye cry (it is the same). His are the most beautiful names. And thou (Muhammad), be not loud-voiced in thy worship nor yet silent therein, but follow a way between.