1 Corinthians 9:16-19

For if I preach the gospel, I have nothing to glory of; for necessity is laid upon me; for woe is unto me, if I preach not the gospel. For if I do this of mine own will, I have a reward: but if not of mine own will, I have a stewardship intrusted to me. What then is my reward? That, when I preach the gospel, I may make the gospel without charge, so as not to use to the full my right in the gospel. For though I was free from all men, I brought myself under bondage to all, that I might gain the more.