His saying—peace and blessings of Allah be upon him—: "The clean soil is the purification of the Muslim, even if he does not find water for ten years. So when you find water, let it touch your skin." Narrated by Abu Dawud and Al-Nasa'i. By its implication (mafhum), it indicates that it is not a purifier when water is present, and by its explicit wording (mantuq), it indicates the obligation of letting it touch his skin when it is present. Furthermore, he has become capable of using water, so his tayammum is invalidated, like one exiting the prayer. Moreover, tayammum is a purification of necessity, so it is invalidated by the removal of the necessity, like the purification of the woman suffering from chronic vaginal discharge (mustahada) when her bleeding ceases. This is verified by the fact that tayammum does not remove the ritual impurity (hadath); rather, it is only permitted for the one performing tayammum to pray while in a state of impurity due to the necessity of inability to use water. When he finds water, the necessity ceases, so the ruling of the impurity becomes apparent, as is the original state. It is not valid to draw an analogy to them [the Shafi'i argument regarding fasting]; for the fast is the substitute itself, so its counterpart is when he becomes able to use water after his tayammum, and there is no disagreement regarding its invalidation. Furthermore, the difference between the two is that the duration of the fast is long, so exiting it is difficult because it involves combining two difficult obligations, unlike our case. Their claim that he is incapable is incorrect; for water is near, his capacity (to use it) is intact, and obstacles are absent. Their claim that he is forbidden from invalidating the prayer: we say that there is no need to invalidate the prayer; rather, it becomes invalid by the cessation of the purity, as is the case in similar examples.

Once this is established, whenever he exits and performs wudu, he is required to restart the prayer. It is said there is another opinion: that he may build upon what has passed of it, like one whom the minor impurity overtakes. The correct view is that he does not build upon it; because purity is a condition, and it has been lost by the invalidation of the tayammum, so it is not permissible for the prayer to remain while its condition is missing, nor is it permissible for what has passed to remain valid while he exits it before its completion. We state the same regarding one whom the minor impurity overtakes. If we were to concede that, the difference between them is that what has passed of the prayer was built upon a weak purity in this instance, so he does not have the right to build upon it, unlike the one whom the minor impurity overtakes.

Section: As for the one who prays according to his state without wudu or tayammum, if he finds water or soil while in prayer, he must exit it in all cases; because it is a prayer performed without purity. It is possible that it be analogized to the case of tayammum when one finds water, if we say that he is not required to repeat it, and because purity is a condition whose consideration has fallen, so it resembles the sutra (barrier) when he is unable to use it, so he prays while naked, then finds a sutra during the prayer near him. Every prayer that he is required to repeat, he is required to exit it when the excuse is removed, and he is required to restart it. If we say he is not required to repeat it, then it resembles the prayer of the one who performed tayammum when he finds water, according to the previous discussion on it.