Babylonian Talmud: Tractate Berakoth
(31a) R. Hamnuna said: How many most important laws can be learnt from these verses relating to Hannah! [I Sam. I, 10ff] Now Hannah, she spoke in her heart🙁עַל-לִבָּהּ) from this we learn that one who prays must direct his heart. Only her lips moved: from this we learn that he who prays must frame the words distinctly with his lips. But her voice could not be heard: from this, it is forbidden to raise one’s voice in the Tefillah. Therefore Eli thought she had been drunken: from this, that a drunken person is forbidden to say the Tefillah.