1 Corinthians 2:4:
and my speech and my message were not in plausible words of wisdom, but in demonstration of the Spirit and of power,
1 Corinthians 4:20:
For the kingdom of God does not consist in talk but in power.
1 Thess. 1:4-5:
4 For we know, brothers loved by God, that he has chosen you,
5 because our gospel came to you not only in word, but also in power and in the Holy Spirit and with full conviction. You know what kind of men we proved to be among you for your sake.
2 Peter 1:21:
For no prophecy was ever produced by the will of man, but men spoke from God as they were carried along by the Holy Spirit.
Is not my word like fire, declares the LORD, and like a hammer that breaks the rock in pieces?