1 Corinthians 9:15-19

But I have used none of these things. And I am not writing these things so that it will be done so in my case; for it would be better for me to die than have any man make my boast an empty one. For if I preach the gospel, I have nothing to boast of, for I am under compulsion; for woe is me if I do not preach the gospel. For if I do this voluntarily, I have a reward; but if against my will, I have a stewardship entrusted to me. What then is my reward? That, when I preach the gospel, I may offer the gospel without charge, so as not to make full use of my right in the gospel. For though I am free from all men, I have made myself a slave to all, so that I may win more.