Regarding the letter that begins with the word “Katonti,” (printed in the Tanya, Iggeres HaKodesh, Epistle 2), it was said in the name of the Rebbe Maharash, passed on to the Rebbe Rashab, who in turn relayed it to the Previous Rebbe, that if the Alter Rebbe (the author) would not have inserted the three words “b’middas emes l’Yaakov,” 1 (“according to the attribute of truth unto Yaakov”) he would have had an additional fifty thousand chassidim, but the Rebbe demands the middah (trait) of emes (truth).

Likkutei Dibburim, vol. 1, p. 104;
HaYom Yom, 10 Menachem Av

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When he would give a letter to a traveler to transport to another city, the Tzemach Tzedek would simultaneously deliver to the post office the current amount of the stamp necessary to send the letter.

Igros Kodesh of the Rebbe, vol. 11, p. 137

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The expression of our Rebbeim is well known: In the face of emes (truth), all become batel (nullified).

Igros Kodesh of the Rebbe, vol. 17, p. 179

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The Previous Rebbe writes that his father, the Rebbe Rashab, said: Truth is the middle path. An inclination to the right — to be overly stringent with oneself and find faults or sins not in accord with the truth; or an inclination to the left — to be overly indulgent, covering one’s faults of leniency in demands of avodah (service) out of self-love — both these ways are false.

HaYom Yom, 27 Adar I