The Holy Rule
Let us do what the Prophet saith: "I said, I will take heed of my ways, that I sin not with my tongue: I have set a guard to my mouth, I was dumb, and was humbled, and kept silence even from good things" (Ps 38:2-3). Here the prophet showeth that, if at times we ought to refrain from useful speech for the sake of silence, how much more ought we to abstain from evil words on account of the punishment due to sin.
Therefore, because of the importance of silence, let permission to speak be seldom given to perfect disciples even for good and holy and edifying discourse, for it is written: "In much talk thou shalt not escape sin" (Prov 10:19). And elsewhere: "Death and life are in the power of the tongue" (Prov 18:21). For it belongeth to the master to speak and to teach; it becometh the disciple to be silent and to listen. If, therefore, anything must be asked of the Superior, let it be asked with all humility and respectful submission. But coarse jests, and idle words or speech provoking laughter, we condemn everywhere to eternal exclusion; and for such speech we do not permit the disciple to open his lips.