Osek b'mitzvah patur min hamitzvah

In Judaism, the concept of Osek B'Mitzvah Patur Min Hamitzvah (עוסק במצוה פטור מן המצוה, rough lt. "engaged in commandment exempt from the commandment", or rather, in a more understandable translation, "one who is engaged in a commandment is exempt from another commandment [at the same time]") sometimes exempts one from performing a religious obligation while one is engrossed in another religious obligation.

Extensions of the Rule
The Talmud makes use of a similar concept in reference to those who are not yet actively engaged in a mitzvah (commandment) but also to those who are busy preparing to perform a mitzvah, with the comment that שלוחי מצוה (shluchei mitzvah, lit. "messengers of a precept") are similarly exempt from performing other religious obligations, such as sitting in a sukkah.

The Pnei Yehoshua comments that such exemptions are valid only for positive commandments, stating that one thoroughly engaged in a positive precept (such as burying the dead or learning Torah) would certainly not enable one to violate negative precepts (such as performing adultery or consuming non-kosher food).