Proverbs 10:18
"He that hideth hatred with lying lips, and he that uttereth a slander, is a fool."
Cross References (ranked by relevance)
The words of his mouth were smoother than butter, but war was in his heart: his words were softer than oil, yet were they drawn swords.
And when Abner was returned to Hebron, Joab took him aside in the gate to speak with him quietly, and smote him there under the fifth rib, that he died, for the blood of Asahel his brother.
He that backbiteth not with his tongue, nor doeth evil to his neighbour, nor taketh up a reproach against his neighbour.
Whoso privily slandereth his neighbour, him will I cut off: him that hath an high look and a proud heart will not I suffer.
Thou sittest and speakest against thy brother; thou slanderest thine own mother’s son.
They speak vanity every one with his neighbour: with flattering lips and with a double heart do they speak.
And Saul was yet the more afraid of David; and Saul became David’s enemy continually.
For there is no faithfulness in their mouth; their inward part is very wickedness; their throat is an open sepulchre; they flatter with their tongue.