Moshe Rabbeinu's Tefillin
Rabbi Sruly Bornstein
In the beginning people thought this Machlokes was like many of the Machlokes between Rashi and Rabbeinu Tam, until the Arizal came and said from a Kabalah he got from Eliyahu Hanavi that both Svaros are Emes, and you have to wear both... and from Moshe until the Geonim they always wore two pairs of Tefillin Sugya: תפילין