1 Corinthians 9:25-27

25Everyone who competes in the games goes into strict training. They do it to get a crown that will not last, but we do it to get a crown that will last forever. 26Therefore I do not run like someone running aimlessly; I do not fight like a boxer beating the air. 27No, I strike a blow to my body and make it my slave so that after I have preached to others, I myself will not be disqualified for the prize.