Musar על יומא 171:12

In one's speaking: our sages, of blessed memory, said: "one should always speak with other people in a gentle manner" (Yomah 86a). This is stated explicitly in scripture: "the words of the wise are heeded [when spoken] gently" (Kohelet 9:17). One's words should be of honoring [others] not of belittling them. Likewise scripture says: "he who belittles his fellow lacks sense" (Mishlei 11:12), and "when the wicked comes, there also comes contempt" (Mishlei 18:3).