فصار فرضًا في حق العمل
Thus, as regards performance, wajib is binding much like fard.
The point is that saying “this is not fard” does not make omission of wajib permissible. The responsible person is required to perform wajib, and unjustified neglect remains blameworthy.
For example, in Hanafi jurisprudence the witr prayer is wajib. It is not established with the definitive status of the five daily fard prayers, but it is not treated as merely voluntary either. Non-definitive proof must not be confused with absence of obligation.