Performing Tayammum on Filthy Earth or Earth Covered by a Layer of Salt
Issue No.647- It is better to avoid performing tayammum on filthy earth, deep earth and roadsides, or the saline earth on which a layer of salt has not settled over. If, however, a layer of salt has covered the earth, tayammum on it is void. If the earth is so filthy that one fears that he would become sick by performing tayammum on it, one should, as an obligatory precaution, offer prayer without tayammum and offer the qaḍā later.
