Amira l’akum--instructing a non-Jew to do forbidden labor (both
mid’oraisa and
mid’rabonon) --is forbidden on
Shabbos and
Yom Tov. For the sake of a
mitzvah, however, one may instruct a non-Jew to do
melacha mid’rabonon. Therefore, a non-Jew may be asked to climb a tree or cross a river to procure a
shofar. Some
poskim even allow instructing a non-Jew to do
melacha mid’rabonon to obtain a better
shofar than the one he has. The
poskim disagree about whether it is permissible to instruct a non-Jew to obtain a
mitzvah object in this manner if it is not clear that he will be successful.
[שו"ע תקפו, כא, משנ"ב פו, ושעה"צ קכ; ביאורים ומוספים דרשו, 80 ,82 ו־83 ,וראה שם, 84]