A traveler performs Tayammum when he suffers from a disease or water is not available

Q: Is it unconditionally permissible to perform Tayammum (dry ablution with clean earth) while traveling even when water is available?

A: All praise be to Allah Alone, and peace and blessings be upon His Messenger, and his family and Companions. It is impermissible for a traveler to perform Tayammum unless they are sick and will be physically harmed by using water, cannot use water, or cannot find water. Allah (Exalted be He) says (what means): O you who believe! Approach not As-Salât (the prayer) when you are in a drunken state until you know (the meaning) of what you utter, nor when you are in a state of Janâba ,(i.e. in a state of sexual impurity and have not yet taken a bath) except when travelling on the road (without enough water, or just passing through a mosque), till you wash your whole body. And if you are ill, or on a journey, or one of you comes after answering the call of nature, or you have been in contact with women (by sexual relations) and you find no water, perform Tayammum with clean earth and rub therewith your faces and hands (Tayammum). Truly, Allâh is Ever Oft-Pardoning, Oft-Forgiving. (Surah Al-Nisa’, 4:43) Allah (Exalted be He) also says: O you who believe! When you intend to offer As-Salât (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 Janâba (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 from the Ghâ'it (toilet), 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. Allâh does not want to place you in difficulty, but He wants to purify you, and to complete His Favour to you that you may be thankful. (Surah Al-Ma’idah, 5:6). Thus, Allah (Glorified be He) has stipulated that purification with water (Wudu’ and Ghusl) is to be substituted by purification with clean earth (Tayammum) in case there is no water. This is because it is authentically reported that the Prophet (peace be upon him) said: “The whole earth has been made for us a Masjid (place of worship), and its soil has been made for us a purifier in case we cannot find water.” (Part No. 5; Page No. 336)  (Related by Muslim). However, it is permissible for the sick, who cannot use water by themselves or even with the help of others or will be physically harmed by using it because of their illness, to perform Tayammum even if water is available. This is because Allah (Exalted be He) says: So keep your duty to Allâh and fear Him as much as you can May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.