1 Corinthians 9:15-18 ESV
But I have made no use of any of these rights, nor am I writing these things to secure any such provision. For I would rather die than have anyone deprive me of my ground for boasting. For if I preach the gospel, that gives me no ground for boasting. For necessity is laid upon me. Woe to me if I do not preach the gospel! For if I do this of my own will, I have a reward, but if not of my own will, I am still entrusted with a stewardship. What then is my reward? That in my preaching I may present the gospel free of charge, so as not to make full use of my right in the gospel.
ESV: English Standard Version 2016