Prayer: Blood Seeping Through Unlined Clothing
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 842
If blood spills on clothing that does not have a lining and it reaches the other side, it is considered to be one blood; and the side on which the blood has spread more must be taken into account [when determining its amount in relation to the area covered by a dirham]. However, if the other side of the clothing becomes bloody separately, then each side must be considered separately. Therefore, if the combined area of blood on the front and back of the clothing is less than the area covered by a dirham, prayers with it are valid; but if it is equal to or more than the area covered by a dirham, then prayers performed with it are invalid.