Shabbat 62A

והתניא, רבי אושעיא אומר: ובלבד שלא יאחזנו בידו ויעבירנו ארבע אמות ברשות הרבים!

But wasn’t it taught in a baraita that R' Oshaya says with regard to an amulet: As long as he does not hold it in his hand and carry it 4 cubits in the public domain? Apparently, even with regard to an amulet, there is a distinction between wearing it and carrying it.

[אלא] הכא במאי עסקינן ⁠— במחופה עור.

Rather, with what are we dealing here? With an amulet that is covered in leather. Since the writing itself is covered, the name of God is not degraded when the amulet is brought into the latrine with him.

והרי תפילין דמחופות עור, ותניא: הנכנס לבית הכסא ⁠— חולץ תפילין ברחוק ארבע אמות ונכנס.

The Talmud objects. There is writing on the scrolls of tefillin, which is covered in the leather of boxes housing the scrolls, and nevertheless it was taught in a baraita: One who enters a latrine while wearing tefillin must remove the tefillin at a distance of 4 cubits and only then enter. There is no halakhic difference whether or not the writing is covered.

התם משום שין. דאמר אביי: שין של תפילין הלכה למשה מסיני. ואמר אביי: דלת של תפילין הלכה למשה מסיני. ואמר אביי: יוד של תפילין הלכה למשה מסיני.

The Talmud rejects this: There, with regard to tefillin, the prohibition to enter the latrine is not due to the sacred writing on the scrolls inside the tefillin. Rather, it is due to the letter shin that protrudes from the leather of the boxes housing the scroll in the tefillin of the head, as Abaye said: The source of the requirement of the shin of the tefillin is a halakha transmitted to Moses from Sinai. It is required by Torah law. And, Abaye said: The knot in the shape of the letter dalet in the straps of the tefillin of the head is a halakha transmitted to Moses from Sinai. And, Abaye said: The letter yod of the tefillin is a halakha transmitted to Moses from Sinai. It is due to those letters that one must safeguard the sanctity of the tefillin and refrain from taking them into the latrine.