Prayer: Doubting Purity and Investigation
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 794
If someone has a doubt about his body or clothing being pure, in the event that he investigates and does not see anything on it and performs prayers, and after prayers, he realises that his body or clothing was impure, his prayers are valid. However, if he does not investigate, then based on obligatory precaution, he must perform his prayer again; and in the event that the time has expired, he must make it up.