1 Corinthians 9:16-18

16 If I proclaim the gospel, this gives me no ground for boasting, for an obligation is laid on me, and woe to me if I do not proclaim the gospel!
17 For if I do this of my own will, I have a reward; but if not of my own will, I am entrusted with a commission.
18 What then is my reward? Just this: that in my proclamation I may make the gospel free of charge, so as not to make full use of my rights in the gospel.
New Revised Standard Version Bible, copyright 1989, Division of Christian Education of the National Council of the Churches of Christ in the United States of America. Used by permission. All rights reserved.