What is the standard for distinguishing between a small and a large amount of impure blood?

Question : He mentions a small amount of impure blood. The word "small" is the opposite of "large." So, what is the standard for distinguishing between a small and a large amount? Is the standard based on each person's own perception? If a person sees something as small, it is small, and if he sees it as large, it is large, and each person consults his own heart? Or is the criterion what has become customary?

Answer : Regarding what people consider large being large, and what they consider small being small, there are two opinions among the scholars in this issue. However, the stronger opinion is that the criterion is the custom of the people: what people consider large is large, and what they consider small is small. This is because if we referred to each person's own perception, the ruling would not be regulated. The person with obsessive doubts would consider a small amount to be large in his eyes, while the negligent person would consider a large amount to be small in his eyes, and regulation would be impossible. If we adopted this opinion, two men might be praying in garments, each with blood on his, and the amount on one would be equal to the amount on the other. We would tell one of them, "Your prayer is invalid," and tell the other, "Your prayer is not invalid." Why? Because the second man considers it small, and the first man considers it large. This is not appropriate for the just Shari'ah. Therefore, the distinction between small and large refers to custom. What people consider large is large. Now, what is an example? For instance, one drop, two drops, three drops, and the like—these are all considered small.