Reference for Bava Metzia 116:4

And so a person [must] remember [this] and take care during his learning the Torah how he speaks the letters of the Torah, for with them was the world created, and by himself attach the letters to their root letters in the Torah, which was given like this to the world through 'thunder and lightening' in order that 'the fear of God should be upon you and you will be without sin', as explained. In any case, if 'awe' and 'fear' befall a person in 'thunder and lightening', its seems apparent that he would not sing, God forbid. For how could there be the possibility of sin with all that. And this is the idea of the 'heavenly voice which goes forth', they are the letter of the Torah inside every person who recalls and declares them daily. And he who doesn't not hear the heavenly voice [and for whom] it is as if he did not declare, 'woe unto him...for insulting the Torah' which is inside of him. And this is the meaning of 'for anyone who does not involve himself in the Torah' meaning - who is not inscribed in the Torah, "he is called "rebuked"'; for this is the idea of rebuke for a person which changes his 'face to redness'