Does seeing signs of water invalidate prior Tayammum when seeking water is obligatory?
Chapter on Tayammum
Al-Mughni
Book of Purification
Primary text
If a person performs Tayammum and subsequently sees riders, greenery, or anything indicating the presence of water in a location where seeking water is obligatory, the Tayammum becomes void. This is the position of Al-Shafi'i, based on the obligation to seek water. The invalidation occurs whether the initial assumption (that water is present) is later proven false or not. The reason for invalidation is tied to the newly established obligation to seek water.
Supporting text
There is an alternative position stating that if the signs of water are seen while already performing prayer, neither the prayer nor the Tayammum is invalidated because the individual began the act with a certain purity, which is not nullified by doubt. Furthermore, it is argued that even outside of prayer, the Tayammum does not become void because the certainty of purity is not overturned by doubt, similar to the ruling regarding water purity. Additionally, the obligation to seek water is not inherently nullifying unless established by specific religious proof, which is absent here.