What is the ruling on the anticipated ritual impurity from gravel splashing onto one's feet and clothes when going out in India, given that one's feet are sweaty?

It is not obligatory to wash shoes, feet, or the bottom of trousers from small pebbles, the impurity of which is doubtful, because the default state of things is purity. This doubt might be a whisper from Satan. However, if the foot is wet with sweat and encounters impure pebbles, it must be washed before prayer, unless what it encountered is considered a small amount by custom, in which case it is pardoned due to hardship. A small amount of impure street mud is also pardoned due to the difficulty of avoiding it, even if it has mixed with dog impurities, because streets are a source of impurities.