Chapter on the Rulings of Tayammum
Allah – exalted is He – has ordained that anyone who wishes to perform the prayer must first remove both minor and major ritual impurity with the water He has sent down as a means of purification. This obligation remains in force whenever water is available. Yet circumstances may arise in which water is entirely absent, practically unobtainable, or present but unusable because of a legitimate excuse. In such cases Allah has provided an alternative: dry ablution with clean earth, thereby easing matters for this Muhammadic community and lifting hardship.
The Almighty says in His definitive Revelation: “O you who believe, when you rise to perform the prayer, wash your faces and your hands up to the elbows; wipe your heads and wash your feet up to the ankles. If you are in a state of major impurity, then purify yourselves. But if you are ill, on a journey, one of you has relieved himself, or you have been intimate with women, and you cannot find water, then seek clean earth and wipe your faces and hands with it. Allah does not wish to burden you; rather, He wishes to purify you and complete His favor upon you, so that you may give thanks.” (Q 5:6)