1 Corinthians 9:25-27

And every man that striveth for the mastery is temperate in all things. Now they [do it] to obtain a corruptible crown; but we an incorruptible.

I therefore so run, not as uncertainly; so fight I, not as one that beateth the air:

But I keep under my body, and bring [it] into subjection: lest that by any means, when I have preached to others, I myself should be a castaway.