After putting such words into our mouth, and maliciously charging Christians with sentiments which they never held, he then proceeds to give to this supposed expression of Christian feeling an answer, which is indeed more a mockery than an answer, when he says, “Do you not see, good sir, that even your own demon is not only reviled, but banished from every land and sea, and you yourself, who are as it were an image dedicated to him, are bound and led to punishment, and fastened to the stake, while your demon— or, as you call him, 'the Son of God'— takes no vengeance on the evil-doer?”
This answer would be admissible if we employed such language as he ascribes to us; although even then he would have no right to call the Son of God a demon. For as we hold that all demons are evil, He who turns so many men to God is in our view no demon, but God the Word, and the Son of God. And I know not how Celsus has so far forgotten himself as to call Jesus Christ a demon, when he nowhere alludes to the existence of any evil demons. And finally, as to the punishments threatened against the ungodly, these will come upon them after they have refused all remedies, and have been, as we may say, visited with an incurable malady of sinfulness.
Source: Against Celsus (New Advent)