Attending a brit at which Shabbat will be violated

Hi,

One is not supposed to put himself into a position where he will witness violation of the laws of Shabbat. However, one should not lose the opportunity for a mitzvah in order to avoid such a place; therefore, a mohel should go to perform a brit milah in a place where people violate Shabbat, and then leave once the mitzvah is done.

(Rav Moshe Feinstein, Igrot Moshe Yoreh Deah 1:156)

Have a great day,
Mordechai