﴿ وَإِن تَجْهَرْ بِٱلْقَوْلِ فَإِنَّهُۥ يَعْلَمُ ٱلسِّرَّ وَأَخْفَى ﴾

“And if thou say anything aloud, [He hears it] since, behold, He knows [even] the secret [thoughts of man] as well as all that is yet more hidden [within him].”

And should you be loud in your speech in remembrance of God or supplication then God has no need for this to be spoken loud then indeed He knows the secret and that which is yet more hidden than that secret namely that which the soul whispers to itself and that which occurs to the mind but which you do not speak of to anyone so do not strain yourself to be loud in your speech.