1 Corinthians 9:16-18

16For when I preach the gospel, I cannot boast, since I am compelled to preach. Woe to me if I do not preach the gospel! 17If I preach voluntarily, I have a reward; if not voluntarily, I am simply discharging the trust committed to me.

18What then is my reward? Just this: that in preaching the gospel I may offer it free of charge, and so not make full use of my rights as a preacher of the gospel.