You shall not be double-minded nor double-tongued, for to be double-tongued is a snare of death. Your speech shall not be false, nor empty, but fulfilled by deed.
Clement of Rome
Let us clothe ourselves in concord, being lowly-minded and temperate, holding ourselves aloof from all backbiting and evil speaking, being justified by works and not by words. For He said, He that said much shall hear also again. Does the ready talker think to be righteous? Blessed is the offspring of woman that lives but a short time. Be not you abundant in words.
And in proportion as a man sees that his bishop is silent, let him fear him the more.
It is better to keep silence and to be, than to talk and not to be. It is a fine thing to teach, if the speaker practice. Now there is one teacher, who “spoke and it came to pass:” yea and even the things which He has done in silence are worthy of the Father. He that truly possesses the word of Jesus is able also to hearken unto His silence, that he may be perfect; that through his speech he may act and through his silence he may be known. – ibid
Shepherd of Hermas
But make these words known to all your children, and to your wife who shall be as your sister; for she too refrains not from using her tongue.
First of all, speak evil of no man, neither take pleasure in listening to a slanderer. Otherwise you that hear too shall be responsible for the sin of him that speaks the evil, if you believe the slander, which you hear; for in believing it you yourself also will have a grudge against your brother. So then shall you be responsible for the sin of him that speaks the evil. – ibid
Clement of Alexandria
For the saying, “It is not a good tree which produces corrupt fruit, nor a corrupt tree which produces good fruit,” is to be applied in this case. For speech is the fruit of the mind. If, then, jokers are to be ejected from our society, we ourselves must by no manner of means be allowed to stir up laughter. For it were absurd to be found imitators of things of which we are prohibited to be listeners; and still more absurd for a man to set about making himself a laughing-stock, that is, but of insult and derision.
Pleasantry (an agreeable playfulness in conversation or good humor) is allowable, not waggery (mischievous humor). Besides, even laughter must be kept in check; for when given vent to in the right manner it indicates orderliness, but when it issues differently it shows a want of restraint. For, in a word, whatever things are natural to men we must not eradicate from them, but rather impose on them limits and suitable times. For man is not to laugh on all occasions because he is a laughing animal, any more than the horse neighs on all occasions because he is a neighing animal. But as rational beings, we are to regulate ourselves suitably, harmoniously relaxing the austerity and over-tension of our serious pursuits, not inharmoniously breaking them up altogether. – ibid
But, on the other hand, one needs not be gloomy, only grave. For I certainly prefer a man to smile who has a stern countenance than the reverse; for so his laughter will be less apt to become the object of ridicule. – ibid
From filthy speaking we ourselves must entirely abstain, and stop the mouths of those who practice it by stern looks and averting the face. – ibid