Blasphemy: Against the Holy Spirit, Unpardonable
Source: TTT
Matthew 12:31, 32
Therefore I tell you, every sin and blasphemy will be forgiven men, but the blasphemy against the Spirit will not be forgiven. / Whoever speaks a word against the Son of Man will be forgiven, but whoever speaks against the Holy Spirit will not be forgiven, either in this age or in the one to come.