Tertullian

“ The sounds of our voice, likewise, should be subdued; else, if we are to be heard for our noise, how large windpipes should we need! But God is the hearer not of the voice, but of the heart, just as He is its inspector. ”

“ What superior advantage will they who pray too loudly gain, except that they annoy their neighbours? Nay, by making their petitions audible, what less error do they commit than if they were to pray in public? ”