Tefillin

The Rebbe urged his Chassidim to buy the finest Tefillin they could afford, written by a truly pious scribe.
(Chayei Moharan 511)

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The Rebbe instructed his followers to don Tefillin of Rashi and Tefillin of Rabbenu Tam every day. Reb Noson expounds on this in Likkutei Halakhos.
(Si’ach Sarfey Kodesh IV, 194; Likkutei Halakhos, Tefillin 5:27-32; ibid. 6:16; also see Shulchan Arukh, Orach Chaim 34:1-2; Pri Eitz Chaim, Sha’ar ha-Tefillin, 9. The differences between the shittos of Rashi and Rabbenu Tam, as well as Shemusha Raba and Ra’avad, are presented with diagrams in Rabbi Avraham Yitzchok Sperling’s Ta’amei ha-Mitzvos, p. 19)