Surah Al-Isra, Verse 110

قُلِ ٱدۡعُواْ ٱللَّهَ أَوِ ٱدۡعُواْ ٱلرَّحۡمَٰنَۖ أَيّٗا مَّا تَدۡعُواْ فَلَهُ ٱلۡأَسۡمَآءُ ٱلۡحُسۡنَىٰۚ وَلَا تَجۡهَرۡ بِصَلَاتِكَ وَلَا تُخَافِتۡ بِهَا وَٱبۡتَغِ بَيۡنَ ذَٰلِكَ سَبِيلٗا١١٠

quli id'ʿū l-laha awi id'ʿū l-raḥmāna ayyan mā tadʿū falahu l-asmāu l-ḥus'nā walā tajhar biṣalātika walā tukhāfit bihā wa-ib'taghi bayna dhālika sabīlan

Say, "Call upon Allāh or call upon the Most Merciful [ar-Raḥmān]. Whichever [name] you call - to Him belong the best names." And do not recite [too] loudly in your prayer or [too] quietly but seek between that an [intermediate] way.