I Corinthians 9:16-18

For if I preach the gospel, I have nothing to boast of, for necessity is laid upon me; yes, woe is me if I do not preach the gospel! For if I do this willingly, I have a reward; but if against my will, I have been entrusted with a stewardship. What is my reward then? That when I preach the gospel, I may present the gospel of Christ without charge, that I may not abuse my authority in the gospel.