The Lord has drawn no essential distinctions between fornication, adultery, and harlotry or prostitution. Each has fallen under His solemn and awful condemnation.
You youths of Zion, you cannot associate in non-marital, illicit sex relationships, which is fornication, and escape the punishments and the judgments which the Lord has declared against this sin. The day of reckoning will come just as certainly as night follows day. They who would palliate this crime and say that such indulgence is but a sinless gratification of a normal desire, like appeasing hunger and thirst, speak filthiness with their lips. Their counsel leads to destruction; their wisdom comes from the Father of Lies.
You husbands and wives who have taken on solemn obligations of chastity in the holy temples of the Lord and who violate those sacred vows by illicit sexual relations with others, you not only commit the vile and loathsome sin of adultery, but you break the oath you yourselves made with the Lord Himself before you went to the altar for your sealing. You become subject to the penalties which the Lord has prescribed for those who breach their covenants with Him.
(Heber J. Grant, Conference Report, Oct. 1942, p. 11)