Matthew 12:26
And if Satan casts out Satan, he is divided against himself. How then will his kingdom stand? The application of the divided-house argument to Satan's kingdom: if the exorcisms are Satan casting out his own demons, Satan's kingdom is self-destructing. The argument is not that Satan's kingdom is good but that the coherence of Satan's kingdom is necessary to explain the Beelzebul charge — and the charge is self-defeating. A self-destructing Satan cannot account for the exorcism.