I want to inquire about something which happens to me much. If I fall in the street, or any other dry place, like the sidewalk, or stairs of a building, or in the market, do my clothes become impure? It should be noted that one is doubtful about the sidewalk, or street, or stairs of a building, in other words, it is pretty sure that they are impure.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

In principle these places are pure. It is confirmed that the Prophet said: "The earth is made for me as a mosque and a pure place [for me to perform the prayer], so whenever it is time to perform the prayer, the people of my nation should perform it." [Al-Bukhari and Muslim] Therefore, you should repel these whispers and doubts in this matter unless you are sure that there is an impurity on the ground or on the stairs, in which case you should act accordingly. If the impurity is dry on the floor in a way that it cannot stain your clothes, then there is no harm in this (i.e. you are not required to do anything), however, if this impurity is wet, then there is no doubt that the part of the clothes that are touched by it, must be washed in order to purify them.  

Allaah Knows best.