1 Corinthians 7:2

Nevertheless, to avoid fornication; in the Greek it is, Because of fornications; the sense of which can be no other than this which our translators give. The word is in the plural number, to signify that that which he meaneth by this term, is all sorts of impurities and uncleannesses, which are the products of the lusts of the flesh. These are sins of that nature and species, that if we cannot choose what in respect of some circumstances would be more convenient, we must balk it, rather than run into such a guilt. The apostle doth therefore determine, that in this case it was every man's duty to marry, and every woman's likewise; the reason of which must be, because God had ordained marriage as a means to bridle men, and restrain them from extravagant lusts. His own wife, her own husband; a clear place against polygamy.