Quran Al-Isra 17:110
قُلِ ٱدۡعُواْ ٱللَّهَ أَوِ ٱدۡعُواْ ٱلرَّحۡمَٰنَۖ أَيّٗا مَّا تَدۡعُواْ فَلَهُ ٱلۡأَسۡمَآءُ ٱلۡحُسۡنَىٰۚ وَلَا تَجۡهَرۡ بِصَلَاتِكَ وَلَا تُخَافِتۡ بِهَا وَٱبۡتَغِ بَيۡنَ ذَٰلِكَ سَبِيلٗا ١١٠
Translation
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.