What does the Bible say about the blasphemy of the Holy Spirit?

In Mark 3:28-30, Jesus speaks about blasphemy against the Holy Spirit, stating that all sins and blasphemies can be forgiven except this particular sin. This is because blaspheming the Holy Spirit involves recognizing and attributing the work of God, done through His Spirit, to the devil or an unclean spirit. This denial of the truth of the Gospel and God's nature leads to a hardening of the heart that can result in eternal separation from God. A true believer cannot commit this sin because they are indwelt by the Holy Spirit and acknowledge the work of Christ.