What invalidates Tayammum performed for minor or major ritual impurity?
Chapter on Tayammum
Al-Mughni
Book of Purification
Primary text
Tayammum for minor ritual impurity (Hadath) is invalidated by everything that invalidates Wudu (ablution). Additionally, it is invalidated by the sight of usable water, the passage of time (exit of the time for prayer), and, according to some scholars of our school, the assumption of the presence of water when it was previously thought to be absent. The primary juristic view maintains that removing an item over which wiping was performed (like a turban or shoe) does not invalidate Tayammum, a position held by all jurists. This is because Tayammum is a purification state where no wiping occurred upon the removed item, thus it does not break like water purity, nor is it equivalent to breaking Wudu through removing something wiped upon, as the permissibility of wiping does not confer the status of one who has wiped.
Supporting text
Some scholars of our school asserted that removing a turban or shoe upon which one was permitted to wipe invalidates Tayammum, citing Imam Ahmad's explicit ruling because it invalidates Wudu, and thus invalidates Tayammum like other invalidators. This view is contradicted because the necessary condition for invalidation—removing something actually wiped upon—is absent here.