ה תפלין ומזוזות מ"ט משום דכתיב בהו (דברים ו, ו) והיו בהוייתן יהו מאי תרגום שכתבו מקרא איכא בשלמא תורה איכא (בראשית לא, מז) יגר שהדותא אלא הכא מאי תרגום איכא
5 What is the reason [why] tefillin and mezuzahs [must be written in Hebrew]? — Because in reference to them it is written, “And they shall be”, (Deuteronomy 6:6) which implies, they shall be as they originally were. What cases are there of Aramaic which can be written in Hebrew? I grant you we find in the Torah “yegar sahaduta” (Genesis 31:47); but here [in the case of tefillin, and mezuzot] what Aramaic is there?