Augustine of Hippo

(Serm. 71, 12, 21) Or else impenitence itself is the blasphemy against the Holy Ghost which hath no remission. For either in his thought or by his tongue, he speaks a word against the Holy Ghost the forgiver of sins, who treasures up for himself an impenitent heart. But he subjoins, Because they said, He hath an unclean spirit, that he might shew that His reason for saying it, was their declaring that He cast out a devil by Beelzebub, not because there is a blasphemy, which cannot be remitted since even this might be remitted through a right repentance: but the cause why this sentence was put forth by the Lord, after mentioning the unclean spirit, (who as our Lord shews was divided against himself,) was, that the Holy Ghost even makes those whom He brings together undivided, by His remitting those sins, which divided them from Himself, which gift of remission is resisted by no one, but him who has the hardness of an impenitent heart. For in another place, the Jews said of the Lord, that He had a devil, (John 7:20.) without however His saying any thing there about the blasphemy against the Spirit; and the reason is, that they did not there cast in His teeth the unclean spirit, in such a way, that that spirit could by their own words be shewn to be divided against Himself, as Beelzebub was here shewn to be, by their saying, that it might be he who cast out devilso.