If ye are ill or on a journey.. And ye find no water, then take for yourselves clean sand or earth and rub therewith your faces and hands. Allah doth not wish to place you in a difficulty, but to make you clean..” (5: 6)
It will be seen from the above mentioned verse of the Holy Quran that permission for resorting to Tayammum is granted on the grounds of illness, travelling and the non-availability of water. It can be performed instead of Wuzu (ablution) or Ghusl (bath). If one is suffering from a disease in which the use of water would be injurious and there are chances that the use of water would aggravate the illness; or if one cannot find water for Wuzu or Ghusl; or if one is travelling in a place where there is no one to indicate where water could be found; or if there is a danger that the enemy might attack while one is performing ablution or taking a bath, then one can perform Tayammum instead of Wuzu or Ghusl.
The approved, traditional method of Tayammum is as under First to recite l and then to make the following niyat:
“I intend to make tayammum with the object of removing impurity and acquiring purity.”
After this, both hands should be struck on some clean and pure earth or sand, the excessive dust blown off and both the hands rubbed on the face in such a way that no part of the face which has to be washed with water in Wuzu is left out. In the case of males, it is desirable to pass the fingers through the beard. Again, both hands should be struck on the clean earth or sand, the excess dust blown off and first the right arm and then the left arm be rubbed unto the elbows. This completes the Tayammum. A dry stone free of dust, brick or an earthen pot may also be used for the purpose. As in the case of Wuzu, several prayers can be said with one Tayammum.
The acts and circumstances which nullify Wuzu also nullify Tayammum. If Tayammum is done because ot the non-availability of water, then it would become ineffectual as soon as water is available. Similarly, if Tayammum was done on account or lllness, then as soon as the disability to use water ceases, Tayammum will become void.