The principle ruling concerning any kind of matter is that of permissibility and purity (That is, they are to be considered permissible and pure unless proven otherwise). If someone, therefore, claims that an object is impure, then the burden of proof is upon him to bring forth some evidence for the impurity of that object.

If he does, his conclusion will be followed. If he is not able to bring forth such proof or if he does not present an acceptable proof, then our judgment will be according to the original principle and it being free of any impurity. Since declaring something to be impure is an obligation that concerns all people, it is not permissible to make such a declaration unless a proof has been established for it. … More CONDENSED FIQH OF TAHARA – HOW TO DO WUDHU – ABLUTION – BATHING – MENSTRUATION – PURIFICATION IN ISLAM EXPLAINED