*Tayammum (Dry Ablution):

It is to resort to Tayammumin the case of the unavailability of water or probability of harm when purification with water might cause harm due to illness, or cause the delay of one’s recovery, or difficulty.

Its description:

When performing Tayammum, one strikes the earth (of the likes such as dust, sand, stone, rock or the like) only once with one’s hands. Then one wipes over his face and hand with the palm of one’s hand.  

Things nullifying Tayammum:

-Whatever nullifies ablution

-Whatever major ritual impurity necessitates ritual bathing

-When water is found (in case Tayammum is performed because of lack of water)

-When there is no longer a legal excuse such as illness and the like.