Is the liquid resembling water (pus) that emerges from a wound impure, and is ablution (wudu') required because of its emergence?

Scholars have differed regarding the invalidation of ablution by fluids from wounds. Some have held that it invalidates ablution if the amount is large, while another group, including Al-Shafi'i and in one narration from Imam Ahmad, maintained that whatever exits from other than the two private parts (front and back) does not invalidate ablution, whether little or much. They cite as evidence that the default state is non-invalidation, and that which is established by a legal proof cannot be removed except by a legal proof.