This excerpt is taken from the book of Fadhilat al-Shaykh Mubashir Ahmad Rabbani, may Allah have mercy on him, Ahkam wa Masail Ramadan.
The fasting person's cupping and the blood flowing from it:
Question:
It is mentioned in the hadith: أفطر الحاجم والمحجوم (The fast of the one who performs cupping and the one who has cupping performed on him is broken). Is this hadith authentic? If it is authentic, what does it mean?
Fatwa:
This hadith is authentic. It has been deemed authentic by Imam Ahmad, may Allah have mercy on him, and several other scholars of hadith. Its meaning is that when a fasting person is cupped by someone else, their fast is broken, and if they themselves are cupped, their fast is also broken because there are two people involved in cupping: the one who performs the cupping and the one who receives it. The one whose blood is drawn is called "Mahjoom," and the one who draws the blood is called "Hajim." If fasting is obligatory, then it is not permissible to undergo cupping unless there is a dire necessity, for example, if one is in great discomfort due to high blood pressure, then there is no harm in cupping because it would be an emergency situation. They will have to make up for that day, as the fast is broken due to cupping; therefore, they can eat and drink for the remainder of the day because a person who breaks their fast due to a legal excuse is permitted to eat and drink for the rest of the day, as the Shariah has allowed breaking the fast on that day, and according to the demands of legal evidence, it is no longer obligatory for them to refrain from eating and drinking.
I would like to mention in relation to this issue that some people think their fast is invalidated due to a small amount of blood coming out from a minor scratch, which is not correct. Rather, we would say that if blood comes out without a person's action, whether it is little or much, it does not break the fast. For example, if someone has a nosebleed and a lot of blood comes out because of it, it does not harm the fast. Or, for instance, if a wound bursts and a lot of blood flows out, the fast is not broken. Similarly, if a person bleeds a lot due to an accident, the fast is not broken because in all these cases, the blood has come out involuntarily. However, if blood is drawn intentionally and it causes weakness in the body and a decrease in strength due to cupping, then the fast will be broken because, in essence, there is no difference between this and cupping. If the amount of blood is so minimal that it does not affect the body, then the fast is not broken. In any case, every person should be aware of the rulings and limits that Allah has revealed to His Messenger, peace be upon him, so that they can worship their Lord with insight.