Musar к Бамидбар 11:23

Therefore, I exhort you to train yourself to sit as much as possible, because the sin of the tongue is the most severe, as our Sages said (Tosefta Pe'ah 1): "These are the things...and lashon hara is equivalent to them all." I don't have to elaborate on this most serious sin of all. "All man's toil is for his mouth" (Koheles 6:7). Our Sages said that all man's mitzvos and teachings are not enough to counterbalance what comes out of his mouth. "What should be a man's pursuit in this world? He should be silent" (Chullin 89a). One must seal his lips as tight as two millstones. Idle words are like powerful weapons which can reach from one end of the world to the other. Now, this is true concerning mere excessive speech. Where forbidden speech is concerned - e.g. lashon hara, mocking, swearing, vowing, fighting and cursing - especially in the synagogue, and on Shabbos and Yom Tov - for every utterance of this type it is impossible to imagine the pain and suffering one will receive (Zohar)! No word is lost; everything is recorded. Winged beings attach themselves to everyone, recording all they say. "For a bird of the skies may carry the sound, and some winged creature may tell the matter" (Koheles 10:20). "Let not your mouth cause your flesh to sin, and do not tell the messenger that it was an error. Why should G-d be angered by your speech and destroy the work of your hands?" (ibid. 5:5). Purchase all your needs through a messenger, even if this would cost two or three times as much. "Is there a limit to what G-d can provide?" (Bamidbar 11:23). Hashem feeds all creatures, from the greatest to the smallest (see A.Z. 3), and provides all their needs. And on Shabbos and Yom Tov do not speak at all about things that are not urgent, and be brief even with what is important, for the Shabbos is very holy and our Sages barely permitted the exchange of greetings on it (Yerushalmi Shabbos, and Tosfos Shab. 113). See how strict they were concerning even a single expression! Continue to give great honor to the Shabbos as when I was there. Do not cut back [on your Shabbos] expenses, since "Man's entire sustenance [for the year is fixed for him from Rosh Hashana to Yom Kippur,] except [the expenditure for Sabbaths and Festivals,] etc." (Beitzah 16a).