Tayammum (Arabic: تيمم) is the Islamic act of dry ritual purification using purified (clean) sand, stone or earth, which may be performed in place of ritual washing (wudu or ghusl) if no clean water is readily available or if one is suffering from moisture-induced skin inflammation or scaling, illness, or hardship.

Tayammum (Arabic: تيمم) is an Arabic word that means an aim or purpose. Tayammum is derived from "amma," meaning 'to repair.'

In Islamic law, Tayammum means to wipe the face and hands of a person with the purpose of purification for prayer by using soil, purified sand, or dust.

Oh you who believe! When you intend to offer As-Salat (the prayer), wash your faces and your hands (forearms) up to the elbows, rub (by passing wet hands over) your heads, and (wash) your feet up to ankles. If you are in a state of Janaba (i.e. after a sexual discharge), purify yourselves (bathe your whole body). But if you are ill or on a journey, or any of you comes after answering the call of nature, or you have been in contact with women (i.e. sexual intercourse), and you find no water, then perform tayammum with clean earth and rub therewith your faces and hands. Allah does not want to place you in difficulty, but He wants to purify you, and to complete His Favor to you that you may be thankful.

In the following eight circumstances, one has to make Tayammum rather than Wudu (ablution) or ghusl (a ritual bath):

O you who have believed, do not approach prayer while you are intoxicated until you know what you are saying or in a state of janabah, except those passing through [a place of prayer], until you have washed [your whole body]. And if you are ill or on a journey or one of you comes from the place of relieving himself or you have contacted women and find no water, then seek clean earth and wipe over your faces and your hands [with it]. Indeed, Allah is ever Pardoning and Forgiving.

Thus, in case of illness, even if there is water, one still does not need to wash.

The verse of tayammum was revealed while Muhammad was on an expedition with the Muslim army and accompanied alongside his wife Aisha. Aisha had borrowed a necklace from Asma, her sister, and had noticed that her necklace was missing. She informed Muhammad about this and he stopped the entire army so that they could look for it. Eventually one of the men found the necklace, however, it was time to pray and no water was to be found for them to perform the wudu (ablution). It was at this point that the verse of Tayammum was revealed.