In the seventh month, on the first day of the month, you shall have a holy convocation; you shall do no laborious work. It shall be a day of teruah for you.
English: It was taught: R. Elazar says, a shofar of idolatry or of an ir hanidachas is valid, even though they are forbidden for benefit — “a day of teruah shall it be for you” is written, from any source.
Type of Learning
Source of the instrument does not disqualify.
What Is Learned
The mitzvah focuses on the sound produced for you, not the object’s history.