1 Corinthians 6:16

6:16 Or do you not know that anyone who is united with a prostitute is one body with her? For it is said, “The two will become one flesh.”

1 Corinthians 7:13-14

7:13 And if a woman has a husband who is not a believer and he is happy to live with her, she should not divorce him. 7:14 For the unbelieving husband is sanctified because of the wife, and the unbelieving wife because of her husband. Otherwise your children are unclean, but now they are holy.