[The Ruling of a Drop from an Impure Vessel Falling into Another Vessel or on Clothing]

Answer (and Allah grants success):
If a drop of blood falls into a vessel of water, the vessel becomes impure; it is not permissible to use it or to purify oneself with it.
If then a drop from that vessel falls into another vessel containing water, the impurity is weakened, and that water becomes majāwir thānī (second-level contact), meaning: pure, but not mutahhir (purifying).
If then a drop from this second vessel falls into a third vessel, that water becomes majāwir thālith (third-level contact), meaning: pure and purifying.
Accordingly:
 If a drop falls on clothing from the first vessel, the clothing is impure.
 From the second vessel: pure.
 From the third: also pure.
This can be supported rationally: the second vessel is further removed from the impurity than the first, and the third vessel further removed than the second. The same applies if a drop of urine falls into a vessel.
So stated some scholars of the madhhab, as in Sharḥ al-Azhār 1.