Answer
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
Tayammum refers to aiming for or seeking soil to wipe one’s face and hands with the intention of preparing oneself to pray, and so on. Tayammum is proven by the Quran, sunnah and ijma`.
In his famous work, Fiqh As-Sunnah, Sheikh Sayyid Sabiq, elaborates on the subject as follows:
What is tayammum?
Literally, tayammum means “aim, purpose.”
In Islamic law, tayammum (dry ablution) refers to “aiming for or seeking soil to wipe one’s face and hands with the intention of preparing oneself to pray, and so on.”
Proof of legitimacy of Is tayammum
The legitimacy of tayammum is proven by the Quran, sunnah and ijma` (consensus).
The Quran says, {And if you are ill, or on a journey, or one of you comes from relieving himself, or you have touched women, and you do not find water, then go to high clean soil and rub your face and hands (therewith). Lo, Allah is Benign, Forgiving.} (An-Nisa’ 4:43)
From the sunnah, Abu Umamah narrated that the Prophet (peace be upon him) said, “All of the earth has been made for me and my nation a pure place of prayer. Whenever a person from my nation wants to pray, he has something with which to purify himself, that is, the earth.” (Related by Ahmad)
Finally, there is a consensus that tayammum forms a legitimate part of the Shari`ah, as it replaces ablution or ghusl under specific circumstances.
Tayammum is a blessing from Allah
This form of ablution is viewed as a blessing from Allah to the Muslims. Jabir relates that the Prophet (peace be upon him) said: “I have been given five things that were not given to anyone before me: I have been made victorious due to fear for a distance of one month’s journey; the earth has been made a place of prayer for me–wherever and whoever of my nation wants to pray, he may pray; and the war booty has been made lawful for me, and this was not lawful for anyone before me. I have been given permission to intercede. The prophets used to be raised for their own people only, but I have been raised for all of mankind.” (Al-Bukhari and Muslim)
Reason for legitimacy of tayammaum
Aishah (may Allah be pleased with her) said: “We went out with the Messenger of Allah on one of his journeys until we reached Baida’. At this place, one of my bracelets broke and fell somewhere. The Messenger of Allah and others began to look for it. There was no water at that place, nor did anyone have any water with him. The people went to Abu Bakr and said, “Do you see what your daughter has done?” Abu Bakr came to me, while the Prophet was sleeping on my thigh. He blamed me and said to me whatever Allah willed him to say. He also poked me in my side. I could not move, for the Prophet was sleeping on my lap. He slept until the morning without any water available. Then, Allah revealed the verse of tayammum. As-Sayyid ibn Huzhain said, ‘That was not the first blessing from the family of Abu Bakr.’ The camel that I was on got up and we found the necklace underneath it.” (Related by “the group,” except for at-Tirmidhi)
Almighty Allah knows best.