Q: How do we understand that the removal of the turban or the khuffs that have been wiped over, invalidate a person's wudhu? They are not listed as invalidators of wudhu. We could say that these items were what made the wudhu valid and the removal of it makes it invalid. But if a person shaves the hair on the head or cuts off nails etc that were part of the wudhu process, we don't say that the wudhu is invalidated. Is there any principle that we are employing here? JazakallahuKhair.
A: If the khuffs are taken off, after having been wiped over, before the expiration time, wudu must be made again. Unlike hair and nails, wiping over the khuffs/turban is an exclusive substitute for washing the feet/wiping the head and so their purification (that of the feet and the head) is invalidated by the substitute being removed much like how tayammum is invalidated once water can be used. Essentially, once any part of the feet or a significant portion of the head becomes exposed, they must be washed just like water must be used once it becomes available. And because the concept of partial invalidation does not exist within the madhhab, the feet cannot be washed, or the head wiped in the case of a turban, without making wudu again even if continuity is maintained.
Source: Sharh al-Muntaha, Kashshaf al-Qina, al-Insaf, al-Mughni