563. Superseding Shabbos

Milah 1:9

When a bris is performed at the proper time, i.e., on the eighth day, it takes precedence over the laws of Shabbos. When not performed at the proper time, it does not take precedence over the laws of Shabbos or yom tov. Regardless of when it is performed, a circumcision supersedes the laws of tzaraas (a skin blemish commonly mistranslated as leprosy). If there was a sign of tzaraas on the foreskin, it may be removed as part of the bris. Even though there is a prohibition against cutting off signs of tzaraas, performing a positive mitzvah takes priority over observing a negative mitzvah.

Milah 1:10

Just as circumcising sons takes priority over the laws of Shabbos, so does circumcising servants who are to be circumcised on the eighth day. The exception to this rule is the case of a servant whose mother only immersed herself after giving birth. Even though this baby is circumcised on the eighth day, his bris does not take precedence over the laws of Shabbos.