Tayammum is done as a substitution for water. The proof for this is Allaah’s saying: “…and you find no water, then perform Tayammum with good earth, wiping your faces and hands with it.” [Surah Al-Maa’idah: 6] And also the Prophet’s (sallAllaahu ‘alayhi wa sallam) saying: “The earth was made a masjid (place of prayer) and purity for me.” [Reported by Al-Bukhaaree and Muslim]
Tayammum is permitted in two situations:
1. When there is no water to be found
Tayammum can be performed for both types of ritual impurities (hadath):
1. Minor Impurity such as urine and feces, and
It is permissible to perform Tayammum with everything that is found on the earth from its various types, such as sand, dirt and other types of earth. This is even if the earth is smooth land and there is no sand or dirt found on it, it is permissible to perform Tayammum on it.
The evidence for this is what has been reported by Jaabir (radyAllaahu ‘anhu) that the Prophet (sallAllaahu ‘alayhi wa sallam) said: “The earth was made a masjid (place of prayer) and a purity for me. So any man from my ummah (nation) who has the time for prayer come upon him, then let him pray, for he has his place of prayer and his purifier with him. So if the prayer time comes upon him and he is in a land in which there is sand or the prayer time comes upon him and he is in a smooth surfaced land, then in this situation, he is ordered to perform Tayammum with this earth.” [Reported by Al-Bukhaaree and Muslim]
Such a person can pray what he wishes from the prayers with this Tayammum, whether the prayer be obligatory or supererogatory. This is because the ruling that Tayammum takes is the same ruling as water. So whatever nullifies one’s wudoo (ablution), then it also nullifies and renders void one’s Tayammum. However, if water is found (and one has Tayammum), something extra is required. So if water becomes available it becomes obligatory for this person to make wudoo (ablution) with it even if his Tayammum hasn’t gotten nullified by one of the factors that cancel out wudoo.
This is based on the hadeeth of Abu Hurairah (radyAllaahu ‘anhu) who said: “Allaah’s Messenger (sallAllaahu ‘alayhi wa sallam) said: ‘The earth serves as the wudoo (ablution) of the Muslim even if he doesn’t find water for ten years. But if he finds water, then he should fear Allaah and let his skin touch it.” This hadeeth was reported by Al-Bazaar and it has a supporting witness from a similar narration of Abu Dharr (radyAllaahu ‘anhu). However, he does not have to repeat the prayers he performed while using that Tayammum.
The description of Tayammum, is that one must first make his intention based on the hadeeth: “Verily, actions are only by intentions.” And then he must mention the name of Allaah (saying Bismillaah). Then he is to strike the earth with his two hands one time and then wipe the palms together along with the back of each hand and his face. This is based on the hadeeth of ‘Ammaar bin Yaasir in which occurs: “He (i.e. Allaah’s Messenger) struck the earth one time and then wiped his left palm on his right palm, the back of his hands and his face.” [Reported by Al-Bukhaaree and Muslim]