Prayer: Mistaking the Category of Impure Blood
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 797
If someone is certain that the blood on his body or clothing is impure blood with which prayers can be performed – for example, he is certain that it is the blood of a wound or a boil – then, in the event that he realises after prayers that the blood was of the type with which prayers cannot be performed, his prayers are valid.