1 Corinthians 5:9
9 I wrote unto you in an epistle not to company with fornicators:
Although it is called First Corinthians, this is not Paul’s first epistle to the Corinthians. He wrote to them earlier about not keeping company with fornicators. This word company means to get mixed up with them. It might even mean to be intimate with them. A fornicator is a sexually immoral person. This church had lots of problems; boasting, pride, and overlooking sexual sins.
Paul’s first letter is lost (for divine reasons) and when it was written is unknown.