Answered by Shaykh Amjad Rasheed
Is there any amount of filth (such as feces, urine, or blood) that does not invalidate one’s prayer?
Urine and Feces
The presence of urine and feces [h: on one’s body, clothes, or place of prayer] is inexcusable [h: and will invalidate one’s prayer], unless it is an extremely small amount that cannot be perceived by the eye.
Great Amounts of Blood
As for blood, if it (1) comes from the person who is praying, (2) is not from an orifice [h: such as the mouth and nose, and (3) is not from one’s own doing], then both small and great amounts are excused [h: and do not invalidate one’s prayer]. If it then spreads through perspiration or affects the garment that one is wearing, it remains excused.
Small Amounts of Blood
As for blood that comes from an orifice (such as the mouth or nose) [h: or blood that flows from one’s body because of one’s own doing], only a small amount is excused. Similarly, if the one praying is affected by someone else’s blood, only a small amount is excused.
How do I know if an amount is “small” or “great”?
“Small” and “great” are determined according to what is commonly acknowledged (urf) as such. So, for example, an amount often affects people or is hard to avoid will be considered “small”.
What if I’m not sure?
If one is uncertain whether an amount is “small” or “great”, it is considered to be “small”.
What if I have small amounts on multiple locations?
If the filth is scattered over many places on the body or clothes of the one who is praying, and [h: the amount of filth on each individual location] is “small”, although if all of it is gathered together it becomes “great”, then according to the relied-upon position (mutamad), it takes the ruling of an amount that is “small” (Tuhfa + Hashiyat al-Sharwani, 1.132).
Amjad Rasheed
Amman, Jordan
(Translated by Hamza Karamali)