wafa al-wafa of samhudi, vol.1 p.94. there is a chapter on carrying the dust or stones of madinah outside for tabarruk: imam nawawi insisted that it is impermissible to carry or take out of the city, the dust and stones from madinah munawwarah. further on the next page samhudi mentions possible reasons they prohibited such things; and also mentioned that people used to take a pinch of dust from the grave of sayyiduna hamza raDiyallahu anhu as medicine. --- on p96, he mentions opinions that suggest that if someone takes them out of the two sanctuaries, they should return (those stones or dust) back to where they belong. ==== Allah ta'ala knows best.