Omitting Namaz Intentionally is Kufr

Shaikh e Sadūq (r.a.) quotes a tradition from Imam Ja’far as-Sadiq (a.s.) wherein it was asked from the Imam (a.s.) why adulterers and drunkards are not called Kafirs while one who omits prayer is labelled so? Imam (a.s.) said, “Adultery etc. are committed when a person is subdued with sensuality but prayer is not omitted except that it was considered insignificant because one who commits adultery, does so to derive pleasure but one who leaves prayer does not get any pleasure.”  Reference : Greater Sins Volume 3