Quotation for Shabbat 215:10

כתנאי מניין למילה שבאותו מקום נאמר כאן ערלתו ונאמר להלן ערלתו מה להלן דבר שעושה פרי אף כאן דבר שעושה פרי דברי ר' יאשיה ר' נתן אומר אינו צריך הרי הוא אומר (בראשית יז, יד) וערל זכר אשר לא ימול את בשר ערלתו מקום שניכר בין זכרות לנקבות

This is a controversy of Tannaim. How do we know that circumcision [must be performed] in that place? 'Orlatho is stated here, and 'orlatho is stated elsewhere: just as there something that produces fruit [is meant], so here too something that produces fruit [is meant]: that is R. Josiah's view. R. Nathan said: It is unnecessary: surely it is said, And the uncircumcised male who is not circumcised in the flesh of his foreskin: — [that indicates] the place where the male sex is differentiated from the female sex. Our Rabbis taught: Tefillin can be written upon the skin of clean animals and upon the skin of clean beasts, and<span class="x" onmousemove="('comment',' Behemah denotes a domestic animal; hayyah, a wild animal. ');">²⁴</span> upon the skin of their nebeloth or terefoth,<span class="x" onmousemove="('comment',' V. Glos. ');">²⁵</span>

Mishnah Kelim