Muslim law excused prayer entirely where purification was impossible

Evidence

If you are prevented from praying, then you should make up at nighttime what you have had to omit during the day; and when ritually pure water is for practical purposes lacking, then you must wipe yourself clean [in the ritually approved fashion—tayammum], even if it is just by rubbing your hands clean on a wall. If that is not possible, the generally held view is that the prayer and its execution are not required in the absence of water or clean stone, although you should make some slight pointing motion with your hands or face toward clean earth or stone or a tree such as would have been ritually acceptable for that purpose (this is as taught by Ibn Naji in his commentary to the Risala, and is based on the Prophet’s words: “Take from them whatever they can bring”). — L. P. Harvey, Muslims in Spain, 1500 to 1614, 322

Categorization

• DEFINE: Tayammum — dry ablution with earth or stone as a substitute for water purification — which here is being applied to the extreme case of crypto-Muslims denied access to any ritual resource.