What is the difference between Fard (obligatory) and Wajib (necessary), and is one who neglects a Wajib not sinful?

The jurists (Usuliyyun) differed concerning the [terms] fard (obligatory) and wajib (definition) (necessary). The majority held them to be synonymous, whereas the Hanafis differentiated between them: Fard is that which is established by a definitive proof, and whoever denies it commits disbelief (kufr). Wajib is that which is established by a speculative proof. According to them, whoever abandons a fard or a wajib is sinful and exposed to punishment. Shaving the beard is forbidden (muharram) according to the Hanafis.