The Torah in the Book of Vayikra says that after a boy is born, "U’bayom Ha’shemini Yimol Besar Orlato" – he undergoes circumcision on his eighth day. The Gemara notes that the verse could have just as easily written, "on the eighth he shall be circumcised," without using the entire phrase, "U’bayom Ha’shemini" ("on the eighth day"). The word "U’bayom" was added, the Gemara explains, to instruct that this command applies even on Shabbat. If a newborn boy’s eighth day falls on Shabbat, the Berit Mila is performed that day despite the fact that several aspects of circumcision – such as cutting the foreskin and drawing blood – ordinarily constitute acts of Shabbat desecration. The Torah makes a special exception allowing Berit Mila on Shabbat despite the prohibitions entailed, provided that Shabbat is the child’s eighth day. If the child was not circumcised on his eighth day, and the Berit is being performed sometime later, the Berit may not be performed on Shabbat.
The entire process of removing the foreskin is permitted on Shabbat in such a case, including those parts of the process which are not indispensable to the performance of the Misva. It goes without saying that all three basic stages of the Berit – the Mila (removal of the foreskin), the Peri’a (removing the thin membrane underneath the foreskin) and the Mesisa (drawing blood from the wound) – are performed when the eighth day falls on Shabbat. However, Halacha even allows a Mohel to remove small pieces of skin that would not disqualify the circumcision if they would remain. As long as the Mohel is still involved in the act of circumcision, and has not stopped, he may remove even these pieces of skin which are removed only as an enhancement, so the Berit will be perfect and complete. One might have assumed that when a Berit takes place on Shabbat, the Mohel should remove only the minimum amount of skin that must be removed for the circumcision to be valid. In truth, however, Halacha allows removing the entire foreskin, even small pieces of skin whose presence would not invalidate the Berit, as long as the Mohel is still involved in the circumcision process and had not stopped.
Furthermore, Halacha allows the Berit to be performed on Shabbat even by two Mohalim. One might have assumed that we should not allow more than one Mohel to circumcise on Shabbat, but Halacha in fact permits inviting two Mohalim to share the Misva by one starting the process and the other completing it. The Mishna Berura (Rav Yisrael Meir Kagan of Radin, 1839-1933) adds that if a second Mohel takes over in the middle of the process, to perform the stage of Peri’a, and the first Mohel – who had removed the foreskin – then notices that he had mistakenly left over some pieces of skin, the first Mohel may go ahead and remove those pieces of skin. Even though he had stopped circumcising, nevertheless, since a second Mohel immediately took over, the first Mohel is considered as still being in the process of circumcising, and so he may complete his stage of the process by removing the small pieces of skin that he mistakenly left.
As we will discuss in future editions of Daily Halacha, it is only the Berit Mila itself which overrides Shabbat. Preparatory stages, such as carrying the knife or the baby through a public domain, do not override the Shabbat prohibitions, even on the child’s eighth day.
Summary: A child is circumcised on his eighth day even if that day is Shabbat. The Mohel performing the circumcision in such a case removes the entire foreskin, and if he sees that he left over some pieces of skin whose presence does not invalidate the circumcision, he may then remove them, too, as long as he is still in the process of circumcising and had not stopped. If one Mohel removed the foreskin and a second Mohel took over for the second stage of the Mila (removing the membrane underneath the foreskin), the first Mohel is still considered to be involved in the process, such that he may return to remove pieces of skin which were mistakenly missed.