Tazria
The Torah teaches us, “On the eighth day, cut the flesh of the foreskin.” This teaches us that even when Shabbos is the eighth day, and causing a wound would normally be forbidden, one is still required to do the bris milah. Chaza”l add that this only applies when one is sure that the eighth day is on Shabbos. When there is a doubt, for example the baby was born during Bein HaShemoshos, one is forbidden from doing so.
Rabbi Aharon Dovid Singer
Rosh Kollel, NMB Kollel
305-972-6508