Prayer: Is It Permissible to Pray in a Masjid Built by Non-Muslims?

Practical Laws of Islam as per the teachings of Imam Khamenei

Prayer: Is It Permissible to Pray in a Masjid Built by Non-Muslims?

Question #418:

Is it permissible to perform prayers in a masjid built by non-Muslims?

Answer #418:

There is no objection to performing prayers in it.

-Imam Khamenei, Practical Laws of Islam, Importance and Conditions of Prayer