6 For the heretics, who are most profane in all things, have sharpened their tongue against the Holy Ghost also, and have dared to utter impious things; as Irenæus the interpreter has written in his injunctions against heresies. For some of them have dared to say that they were themselves the Holy Ghost—of whom the first was Simon, the sorcerer spoken of in the Acts of the Apostles; for when he was cast out, he presumed to teach such doctrines: and they who are called Gnostics, impious men, have spoken other things against the Spirit, and the wicked Valentinians again something else; and the profane Manes dared to call himself the Paraclete sent by Christ. Others again have taught that the Spirit is different in the Prophets and in the New Testament. Yea, and great is their error, or rather their blasphemy. Such therefore abhor, and flee from them who blaspheme the Holy Ghost, and have no forgiveness. For what fellowship have you with the desperate, you, who art now to be baptized, into the Holy Ghost also? If he who attaches himself to a thief, and consents with him, is subject to punishment, what hope shall he have, who offends against the Holy Ghost?
Source: Catechetical Lectures (New Advent)