Prayer: Realising Impurity During Prayer When Time is Short
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 792
If a person starts performing a prayer when time is short, and during it he realises that his clothing has become impure, and he deems it probable that it had become impure after he started the prayer, then, in case his prayer would not be broken up by washing or changing his clothes or taking them off, and he can remove them, he must wash his clothes, change them, or take them off – as long as another thing covers his private parts – and he must then complete his prayer. However, if nothing else covers his private parts and he cannot wash or change his clothes, he must complete his prayer with the impure clothing.