Reference for Menachot 64:2
ואיבעית אימא שינה בזה ובזה תנאי היא דתניא שינה בזה ובזה פסול ר' [אחא מכשיר משום רבי] אחאי ברבי חנינא ואמרי לה משמיה דרבי עקיבא ברבי חנינא
For it was taught: If one did otherwise in either case,<span class="x" onmousemove="('comment',' I.e., both as regards the tefillin and the mezuzah.');"><sup>2</sup></span> it is invalid; R'Ahai declares it valid on the authority of R'Ahai B'R'Hanina (others say, On the authority of R'Jacob B'R'Hanina.) Again, if it were permitted to bring down what is of a higher sanctity to a lower sanctity, [you say that] one would be allowed to make [a mezuzah out of tefillin]?
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