As we have a lot of questions asking about the validity of a prayer due to something expected or assumed to be a najasa النجاسة and many questioners seem to confound tahara الطهارة with cleanness and najasa النجاسة with dirtiness, here some examples:
What dirty (but ritually clean) surfaces can you pray on?
What stains make a prayer invalid
Is my prayer valid given that I wore pants which were dirtied by water splashed onto them by a passing car?
I thought it might make sense to ask a rather general question (similar to Which things break the wudu?) so that we might be able to refer to it later.
I'd like to ask what things are considered to be najis نجس or among the najasaat النجاسات in all approved fiqh schools?
I know that there might be details, but to some extent we may find alcohol, urine and excrement as common in all schools (and Allah knows best).
P.S. to our Shi'a brothers and sisters: In many if not most of my questions I've been hoping for answers from your side!