In Q.5:7, Allah says, 'if ye are ill or on a journey ... and ye find no water, then perform ...'

In Quran 5:7, Allah instructs that if you are ill or traveling and cannot find water to perform wudū (ablution), then you should perform at-tayammum (dry ablution) instead. Wudū is the act of cleaning specific parts of the body with water before performing prayer, which is required for Muslims. However, if water is not available due to illness or traveling, at-tayammum can be performed instead. At-tayammum involves using clean earth or sand to wipe the face and hands. It serves as a substitute for wudū and allows Muslims to fulfill their obligation to perform prayer even when water is not available. Qasr, on the other hand, refers to shortening the length of prayers during travel, and al-ghusl is a full-body washing ritual performed after sexual intercourse or other specific situations.