any of them to wash semen off or rub it off. Does cleansing oneself with stones merely reduce the impurity, or does it purify the area?

There are two well-known views on this. If it is held that it purifies the area, there is nothing further to discuss. If, however, it is held that it merely reduces the impurity, then its remaining traces are excused out of necessity, both where they remain and wherever avoiding them is difficult. Semen is therefore accorded the same ruling as the bodily outlet. And Allah knows best.

He—may Allah have mercy on him—was asked:

“If water from an opening falls onto someone’s clothing, and he does not know its nature, must he wash it off?”

He answered:

He is not required to wash it off. Indeed, according to the correct view, doing so is not even recommended. Likewise, according to the correct view, it is not recommended to ask about it. ‘Umar ibn al-Khattāb was once passing by with a companion when water dripped onto his companion from a waterspout. His companion said:

“Owner of the waterspout, is your water pure or impure?”

‘Umar said:

“Owner of the waterspout, do not tell him, for he is not required to know this.”

And Allah knows best.