Shabbat 79B

קלף כדי לכתוב עליו פרשה קטנה. ורמינהו, קלף ודוכסוסטוס כדי לכתוב עליו מזוזה! מאי ״מזוזה״⁠ — מזוזה שבתפילין. וקרי להו לתפילין ״מזוזה״? אין, והתניא: רצועות תפילין עם התפילין מטמאות את הידים, בפני עצמן ⁠— אין מטמאות את הידים. רבי שמעון בן יהודה אומר משום רבי שמעון: הנוגע ברצועה ⁠— טהור, עד שיגע בקציצה. רבי זכאי משמו אומר: טהור עד שיגע במזוזה עצמה.

We learned in the Mishnah: The measure that determines liability for carrying out parchment is equivalent to that which is used to write the shortest portion in the tefillin. And the Talmud raised a contradiction from that which was taught: The measure that determines liability for carrying out parchment and dokhsostos is equivalent to that which is used to write a mezuza on it. The Talmud asks: What is the meaning of mezuza in this context? It means those Torah portions of the mezuza that also appear in the tefillin. The Talmud asks: And are the tefillin called mezuza? The Talmud answers: Yes, as it was taught in a baraita: The straps of the tefillin, when they are with the tefillin, render the hands ritually impure as is the case with regard to contact with any sacred texts. When they are on their own, they do not render the hands ritually impure. R' Shimon ben Yehuda says in the name of R' Shimon: One who touches the strap of the tefillin remains ritually pure even if it is attached to the tefillin, unless he touches the actual box of the tefillin. R' Zakkai says in R' Shimon’s name: One remains ritually pure until he touches the mezuza itself. Apparently the Torah portions in tefillin are called mezuza.

והא מדקתני סיפא קלף כדי לכתוב עליו פרשה קטנה שבתפילין, שהיא ״שמע ישראל״, מכלל דרישא במזוזה עצמה עסקינן! הכי קתני: קלף ודוכסוסטוס שיעורן בכמה? דוכסוסטוס ⁠— כדי לכתוב עליו מזוזה. קלף ⁠— כדי לכתוב עליו פרשה קטנה שבתפילין שהיא ״שמע ישראל״.

The Talmud asks: And from the fact that the latter clause of the Mishnah teaches: The measure that determines liability for carrying out parchment is equivalent to that which is used to write the shortest portion in the tefillin, which is the portion of Shema Yisrael, by inference, in the first clause of the Mishnah we are dealing with a mezuza itself. Rather, this is what it teaches: With regard to parchment and dokhsostos, how much is the measure that determines liability for carrying them out? The measure that determines liability for carrying out dokhsostos is equivalent to that which one uses to write a mezuza on it. The measure that determines liability for carrying out parchment is equivalent to that which one uses to write on it the shortest passage that is in the tefillin, which is Shema Yisrael.