Sirach 5:14
Ben Sira, Ecclesiasticus12 If you know what to say, answer your neighbor; but if not, put your hand over your mouth. 13 Honor and dishonor come from speaking, and the tongue of mortals may be their downfall. 14 Do not be called double-tongued and do not lay traps with your tongue; for shame comes to the thief, and severe condemnation to the double-tongued. 15 In great and small matters cause no harm,
Didache 2:4
2 You shall not murder; you shall not commit adultery; you shall not engage in sodomy; you shall not commit fornication; you shall not steal; you shall not practice magic; you shall not use love potions; you shall not cause abortion, nor kill newborns; you shall not desire your neighbor's possessions. 3 You shall not commit perjury; you shall not lie; you shall not speak ill; you shall not bear grudges. 4 You shall not be double-minded or speak with a double-tongue, for to do so leads to death. 5 Your words shall not be false or meaningless but followed by actions. 6 You shall not be greedy or exploitative, nor a hypocrite, nor evil-minded, nor arrogant, you shall not plan evil against your neighbor.
Notes and References
"... It is specifically this duality of speech that biblical tradition rejects. This rejection was carried on in later Judaism (the apocryphal work Sirach 5:14 speaks of the 'double-tongued sinner') and Christianity (e.g., Didache 2:4, 'Do not be double-minded nor double-tongued, for the double tongue is a snare of death') ..."
Davids, Peter H. James (p. 90) Baker Publishing Group, 2011