1 Corinthians 9:19 (KJV)

Even so hath the Lord ordained that they which preach the gospel should live of the gospel.

But I have used none of these things: neither have I written these things, that it should be so done unto me: for it were better for me to die, than that any man should make my glorying void.

For though I preach the gospel, I have nothing to glory of: for necessity is laid upon me; yea, woe is unto me, if I preach not the gospel!

For if I do this thing willingly, I have a reward: but if against my will, a dispensation of the gospel is committed unto me.

What is my reward then? Verily that, when I preach the gospel, I may make the gospel of Christ without charge, that I abuse not my power in the gospel.

And unto the Jews I became as a Jew, that I might gain the Jews; to them that are under the law, as under the law, that I might gain them that are under the law;

To them that are without law, as without law, (being not without law to God, but under the law to Christ,) that I might gain them that are without law.

To the weak became I as weak, that I might gain the weak: I am made all things to all men, that I might by all means save some.

And this I do for the gospel's sake, that I might be partaker thereof with you.

Know ye not that they which run in a race run all, but one receiveth the prize? So run, that ye may obtain.