How can one use stones for purification when they are najis (impure) due to the possibility of dust, urine, or feces being on them, and did the Messenger of Allah, may Allah bless him and grant him peace, wash the stone before using it?

The Ahadith have indicated the permissibility of using stones for istijmar (cleaning after defecation) as a means of облегчение (alleviation), even though istinaj (cleaning with water) is better for more complete purification. As for the possibility of a stone being impure from another person having used it for istijmar, this should not be given attention, because the default assumption is its purity, and certainty is not removed by doubt. Washing a stone for istijmar is a blameworthy form of waswasah (obsessive whispering), unless one is certain of its impurity, in which case it is not permissible to use it for istijmar except after purifying it.