There are various places...the most straightforward one that I know is:
1st Corinthians 6:9, 10-- What! Do YOU not know that unrighteous persons will not inherit God’s kingdom? Do not be misled. Neither fornicators, nor idolaters, nor adulterers, nor men kept for unnatural purposes, nor men who lie with men, 10) nor thieves, nor greedy persons, nor drunkards, nor revilers, nor extortioners will inherit God’s kingdom.
It would be covered under fornication.
Other places include:
Proverbs 5:15-23--Drink water out of your own cistern, and tricklings out of the midst of your own well. 16) Should your springs be scattered out of doors, [your] streams of water in the public squares themselves? 17) Let them prove to be for you alone, and not for strangers with you. 18) Let your water source prove to be blessed, and rejoice with the wife of your youth, 19) a lovable hind and a charming mountain goat. Let her own breasts intoxicate you at all times. With her love may you be in an ecstasy constantly. 20) So why should you, my son, be in an ecstasy with a strange woman or embrace the bosom of a foreign woman? 21) For the ways of man are in front of the eyes of Jehovah, and he is contemplating all his tracks. 22) His own errors will catch the wicked one, and in the ropes of his own sin he will be taken hold of. 23) He will be the one to die because there is no discipline, and [because] in the abundance of his foolishness he goes astray.
(Jehovah is God's name according to Psalms 83:18 of the Old King James Version of the Bible)
Hebrews 13:4--Let marriage be honorable among all, and the marriage bed be without defilement, for God will judge fornicators and adulterers.
Revelation 21:8--"But as for the cowards and those without faith and those who are disgusting in their filth and murderers and fornicators and those practicing spiritism and idolaters and all the liars, their portion will be in the lake that burns with fire and sulphur. This means the second death.”
Don is right, the geneological line that Jesus came from has Rahab the prostitute in it. Actually, I am suprised that he didn't mention the fact that Bathsheba, the woman with whom King David had an extramarital affair, was also in that line (she was the mother of King Solomon).
But he would do well to remember that the God of the Bible does forgive readily, as long as the change is made in the person also. But if you know beforehand what God's principles are, then follow them. If you found out after you had committed the sin, then stop committing the sin.
In fact, let's continue reading the scripture from 1st Corinthians stated above.
1st Corinthians 6:9-11--What! Do YOU not know that unrighteous persons will not inherit God’s kingdom? Do not be misled. Neither fornicators, nor idolaters, nor adulterers, nor men kept for unnatural purposes, nor men who lie with men, 10) nor thieves, nor greedy persons, nor drunkards, nor revilers, nor extortioners will inherit God’s kingdom. 11) And yet that is what some of YOU were. But YOU have been washed clean, but YOU have been sanctified, but YOU have been declared righteous in the name of our Lord Jesus Christ and with the spirit of our God.
Notice: Paul notes in this scripture that some of the very Christians he was speaking to had been any and all of those things, including adulterers and fornicators. But they were washed clean and sanctified; and the same was true of Rahab, Bathsheba, and David.