Mark 3:29-30

29but whoever blasphemes against the Holy Spirit and His power [by attributing the miracles done by Me to Satan] never has forgiveness, but is guilty of an everlasting sin [a sin which is unforgivable in this present age as well as in the age to come]”—

30[Jesus said this] because the scribes and Pharisees were [attributing His miracles to Satan by] saying, “He has an unclean spirit.”