I Corinthians 9:14-17

Even so the Lord has commanded that those who preach the gospel should live from the gospel. But I have used none of these things, nor have I written these things that it should be done so to me; for it would be better for me to die than that anyone should make my boasting void. 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.