This is one of them:

Don’t you realize that your bodies are actually parts of Christ? Should a man take his body, which is part of Christ, and join it to a prostitute? Never! And don’t you realize that if a man joins himself to a prostitute, he becomes one body with her? For the Scriptures say, “The two are united into one.” But the person who is joined to the Lord is one spirit with him. (1. Corinthians 6:15-17 NLT)

There are many Christians who have reached the conclusion, and thus given pastoral counseling based on these scriptures, telling two people who have had sexual intercourse that they now must get legally married since they have already become “one” in God’s sight by having sex with each other.

This is an absolute wrong and ridiculous conclusion that has hurt many in the body of Christ; forcing people to get into a marriage that God never meant for them to be in, with devastating [...]