Hebrews 13:4

Marriage is honourable in, or for, all sorts of persons, clergy as well as laity, though the Romanists teach otherwise; and the bed undefiled Consistent with the highest purity. For who can imagine that God would make any thing morally evil absolutely necessary for the support of the human race in future generations? But whoremongers and adulterers God will judge That is, punish, and frequently does so in a very awful manner, even in the present world; though they frequently escape punishment from men. The distinction between these two characters, whoremongers and adulterers, is well known to be this: that the former are single persons who have unlawful converse with one another, and the latter are those who are both, or at least one of them, in a married state. The sin of the first is fornication, of the other adultery; although the word πορνεια, fornication, may sometimes be used to denote any uncleanness, and so to comprise adultery also.