The sin of a person who tells a lie against the Prophet (saws)

Narrated Abu Huraira: The Prophet (sallallahu 'alaihi wa sallam) said, "Name yourselves with my name (use my name) but do not name yourselves with my Kunya name (i.e. Abul Qasim). And whoever sees me in a dream then surely he has seen me for Satan cannot impersonate me. And whoever tells a lie against me (intentionally), then (surely) let him occupy his seat in Hell-fire."