Obligations In Wuzu And Ghusal
Rasool PBUH did not declare to rinse mouth and put water in the nose as Farz or compulsory although he used to do it. To declare something Farz needs more qualifications than mere act of the prophet. Because the act of the prophet can have other meaning that he used to do a thing as it was good ( Mustahab) but not compulsory. He used to say Nawafil regularly, but we know they were never made Farz. However, for Ghusal of Janabat, the word Ittahharu and Taghtasilu, are used which means one should take good care of the act of ghusal and putting water in mouth and nose accomplish it.