Jeremiah 9:3-5, 8

And they bend their tongue, as it were their bow, for falsehood; and they are grown strong in the land, but not for truth: for they proceed from evil to evil, and they know not me, saith Jehovah. Take ye heed every one of his neighbor, and trust ye not in any brother; for every brother will utterly supplant, and every neighbor will go about with slanders. And they will deceive every one his neighbor, and will not speak the truth: they have taught their tongue to speak lies; they weary themselves to commit iniquity.

Their tongue is a deadly arrow; it speaketh deceit: one speaketh peaceably to his neighbor with his mouth, but in his heart he layeth wait for him.