Prayer: Mistaking Impure Blood for Pure Blood
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 796
If someone sees some blood on his body or clothing and is certain that it is not impure blood – for example, he is certain that it is the blood of a mosquito – then, in the event that, after prayers, he realises that it was a type of impure blood with which prayers cannot be performed, his prayers are valid.