Answered by Shaykh Yusuf Weltch
If you recently washed your foot, it’s still wet, and a drop of impure water fell on it. Do the whole foot and the slipper become impure? Is the specific place impure where the drop fell or the entire area? Is it ok to wash that particular place only?
If a bathroom floor I know is impure because people walk in it with their impure slippers if water falls on it and a few drops come on me, but I can’t see any impurity on the floor such as feces or urine, but I know it’s impure. Are these drops excused, or do I have to wash them?
In the Name of Allah, the Most Merciful and Compassionate
If the drop of impure water fell on one’s foot, whether that foot is wet or not, only the place where the impurity contacted the foot is impure. Washing only the contact point of the impurity is sufficient to attain purity. [Shurunbulali, Maraqi al-Falah]
Impurities on Surfaces
The bathroom floor or any other surface is impure if the actual impurity falls upon it. If impurity did come in contact with the floor, only the place of connection is impure.
Once the impurity has dried on the floor, it does not transfer. That is, unless water comes in contact with it or a soaking wet foot. However, the soaked wet foot is only considered impure if traces of the impurity are clearly visible on foot. Traces are the color and/or smell. [Shurunbulali, Maraqi al-Falah]
Everything is Pure until Proven Impure
The floor is pure if you cannot see any impurity on the floor. There is no need for conjecture, assumptions, or even investigating. It is not common for people to urinate or defecate on the floor; that’s why we will ignore any contrary belief.
Unless one sees actual traces of impurity, one should act as if it’s pure. We are not responsible for anything beyond that. Allah Most High says, “and He (Allah) has not placed upon you in the religion any undue hardship.” [Quran, 22:78]
Hope this helps
And Allah knows best
[Shaykh] Yusuf Weltch
Checked and Approved by Shaykh Faraz Rabbani