Matthew 12:31

Luke 12:10 NIV
And everyone who speaks a word against the Son of Man will be forgiven, but anyone who blasphemes against the Holy Spirit will not be forgiven.

Mark 3:28-30 NIV
Truly I tell you, people can be forgiven all their sins and every slander they utter, but whoever blasphemes against the Holy Spirit will never be forgiven; they are guilty of an eternal sin.” He said this because they were saying, “He has an impure spirit.”