Answered by Shaykh Hamza Karamali, SunniPath Academy Teacher
One of the types of filth mentioned in the Reliance is blood. Whenever I buy meat, it has blood on it. Is this blood considered filth?
In the Name of Allah, Most Merciful and Compassionate
Blood on meat does fall under the category of filth. However, it is excused filth (mafuww anhu), meaning that one can cook the meat and eat it without having to wash off the blood. If one adds water to the meat for cooking purposes, and the water changes because of contacting the blood on the meat, this water may likewise be consumed.
There is a caveat, though: if one pours water on the meat with the intention of washing off the blood, the blood is no longer excused (because it has come into contact with a foreign substance) and one must wash it off completely until all its traces are gone. Slight traces that are hard to remove remain excused.
(Fath al-Allam bi Sharh Murshid al-Anam, 1.359; Hashiyat Abd al-Hamid ala Tuhfat al-Muhtaj, 1.293)
And Allah knows best.
Hamza.