1 Corinthians 9:26-27

Amplified Bible

²⁶ Therefore I do not run without a definite goal; I do not flail around like one beating the air [just shadow boxing]. ²⁷ But [like a boxer] I strictly discipline my body and make it my slave, so that, after I have preached [the gospel] to others, I myself will not somehow be disqualified [as unfit for service].