1 Corinthians 6:18

Every sin that a man doeth is without the body That is, every other sinful act which affects the body approaches it from without and affects particular members. But this sin takes the body itself as a whole and makes it an instrument of sin. For it is a violation of the fundamental law impressed upon man from the beginning, whereby it is decreed that a man shall cleave to his wife, and to her alone, and they twain shall be, or rather, becomeone flesh, Genesis 2:24. This view is confirmed by the fact that the word here translated sinneth, means "to go astray," "to miss the mark;" so that the words - sinneth against his own body" imply the running counter to the objects for which the body is created. If this be the correct interpretation of the passage, the practice of polygamy is here condemned.

sinneth against his own body Cf. Romans 1:24.