Tayammum is a dry ablution performed using purified dust or sand when water is unavailable for ritual washing (wudu'). Tayammum can be performed if there is no clean water readily available, to save water for later use, if one is sick and water could worsen their illness or delay cure, or if one has no access to water. To perform tayammum, one intends to prepare for prayer, strikes their hands on earth or dust, shakes off particles, and wipes their face and hands. Tayammum is nullified if water becomes available, necessities requiring bathing occur, or reasons for performing it disappear or are interrupted, such as passing wind.