That remission cannot in the Church be granted unto him who has sinned against God (i.e., the Holy Ghost)
In the Gospel according to Matthew: “Whosoever shall say a word against the Son of man, it shall be forgiven him; but whosoever shall speak against the Holy Ghost, it shall not be forgiven him, neither in this world nor in the world to come.” Also according to Mark: “All sins shall be forgiven, and blasphemies, to the sons of men; but whoever shall blaspheme against the Holy Ghost, it shall not be forgiven him, but he shall be guilty of eternal sin.” Of this same thing in the first book of Kings: “If a man sin by offending against a man, they shall pray the Lord for him; but if a man sin against God, who shall pray for him?”
Source: The Treatises of Cyprian (New Advent)