Prayer: Realising the Mosque is Impure During Prayers
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 1148
If while performing prayers one realises that the mosque is impure, in the event that the time remaining is short, he must complete his prayers. However, if there is ample time and purifying the mosque would not break up the prayer, he must purify it while in prayers and then perform the rest of the prayer. If the prayer would be broken up, then in case it is possible to purify the mosque, it is permitted to break the prayer to purify it. If purifying the mosque after prayers is not possible, he must break his prayers, purify the mosque, and then perform prayers.