"Who mocks the poor insults his Maker; he who rejoices at their calamity will not go unpunished. " ~~ Proverbs (Mishle) 17:5
"The man who slanders hurts three people: the man slandered, the man to whom the slander is uttered—and himself." ~~ Talmud, Arakin 15b
"Whose heart is narrow has a broad tongue. " ~~ Mivchar Hapeninim
"Judge a man only by his own deeds and words; the opinions of others can be false. " ~~ Talmud
"Death and life are in the power of one’s tongue. " ~~ Proverbs (Mishle) 18:21
"Words are the guide to acts: the mouth makes the first move." ~~ Leone Da Modena
"Praising the wicked is wrong. " ~~ Talmud, Sota
"The gossiper has no remedy but to ask for pardon from every one of whom he gossiped, and appease him. " ~~ Harokeach HaKatan
"You can say the nastiest things about yourself without offending anyone." ~~ Phyllis Diller
"Honor and shame are in the power of the tongue. " ~~ Ben Sira 5:15
"As long as I do not utter a word, I am its master; once I utter it, I am its slave." ~~ (based on) Ibn Gabirol
"If you believe all gossip around you, you will be left without one good friend. " ~~ Ben Shlomo Immanuel