Shabbat 132 - Circumcision can be done on Shabbat
All agree that circumcision can be done on Shabbat, although one makes a wound. Rabbi Eliezer allows even preparations for the mitzvah to be done on Shabbat, and the Sages say that any preparation that can be done before Shabbat should be done then - this is the rule of Rabbi Akiva - but all agree on the basic fact. Why is that?
If you say that this is because the circumcision is called a "sign," then I will answer that tefillin are also called a "sign," and they are not worn on Shabbat. If you tell me that it is because circumcision is called a "covenant," then why this "covenant" for an adult is not done on Shabbat? And if you say that it is because it is for "generations," then why tzitzit, which is also "for generations," not made on Shabbat? Rather, it is because circumcision is special in that it has all three of these terms applied to it.
However, Rabbi Yochanan found a simpler explanation. Since the Torah tells to perform circumcision "on the eighth day," this means even if this falls out on Shabbat.
Art: William Blake - The Circumcision