Simeon ben Shetah said: "Examine the witnesses diligently and be cautious in thy words lest through them they learn to falsify." --Avot 1:9

“You shall be sincere with the L-d your G-d.” --Deuteronomy 18:13

“Keep your tongue from evil, and your lips from deceitful speech.” --Psalms 34:14

“Accustom your tongue to say, 'I do not know.'” --Talmud, Berachos 4a

“Correct yourself first, and then you can correct others.” --Talmud, Bava Metzia 107b

“Keep your distance from falsehood.” --Exodus 23:7

“Foolishness is joy to one who lacks [an understanding] heart, but a man of understanding [will rejoice] when he walks uprightly.” --Proverbs 15:21

“Do not offer vain testimony against your fellow, to denar yourself with your lips. Do not say,'As he has done for me, so will I do for him; I will reward the man according to his acts.'” --Proverbs 24:28

“One who deceives his fellow through flattery is spreading a net for his own footsteps.” --Proverbs 29:5