Tayammum replaces wudu or ghusl when water cannot be found or cannot be used because of illness. The Quran says: if you do not find water, then seek clean earth and wipe your faces and hands with it (5:6). The Prophet ﷺ said that the earth was made a place of prayer and a means of purification.
1When it is allowed
No water is available after a reasonable search, or it is available only at a price that is beyond the person's means.
Using water would harm the person because of illness, a wound or severe cold, or would delay recovery.
The water that is present is needed for drinking, for oneself or for others, and there is not enough for both.
2How to do it
Make the intention to use it for the prayer or for the purification that is needed.
Strike clean earth with both palms (once in the hadith of Ammar), and blow off the extra dust.
Wipe the face, and then the backs of the hands, as in the hadith of Ammar.
3What cancels it
Everything that breaks wudu breaks tayammum.
Finding water, or being able to use it, before the prayer. If the water is found after the prayer, the prayer stands and need not be repeated.
Where the schools differ
The four Sunni schools agree on the main ruling above and differ in these points. No school is preferred here.
What is allowed to wipe with. the Hanafi school allows anything from the earth's kind, including stone and sand. The Shafi'i and Hanbali schools require earth with dust. The Maliki school allows anything on the surface of the ground.
The strikes and the arms. the Hanafi and Shafi'i schools say two strikes, with the arms wiped up to the elbows. The Hanbali school says one strike, wiping the face and the palms, as in the hadith of Ammar. In the Maliki school two strikes, with the wrists obligatory and the elbows recommended.
O you who have believed, when you rise to [perform] prayer, wash your faces and your forearms to the elbows and wipe over your heads and wash your feet to the ankles. And if you are in a state of janabah, then purify yourselves. But 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 do not find water, then seek clean earth and wipe over your faces and hands with it. Allah does not intend to make difficulty for you, but He intends to purify you and complete His favor upon you that you may be grateful.
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.
From the Sunnah
Sahih al-Bukhari 335Authentic collection
The point of the hadith: The Prophet ﷺ said that the earth was made for him a place of prayer and a means of purification.
This is general information, not a fatwa. For your own situation, ask a qualified scholar.
Fiqh questions
Tayammum (dry ablution): when it is allowed and how to do it
Tayammum replaces wudu or ghusl when water cannot be found or cannot be used because of illness. The Quran says: if you do not find water, then seek clean earth and wipe your faces and hands with it (5:6). The Prophet ﷺ said that the earth was made a place of prayer and a means of purification.
Is this a fatwa?
No. It is a summary of well-known rulings with their evidence. For your own case, ask a qualified scholar.
What if my school differs from this answer?
Follow the view of the school you follow and the scholar who teaches you. The page lists the differences of the four schools.