Many christians think that sex outside marriage is a sin. What about concubines? Abraham and David had concubines.
Is it a sin to have sex with concubines you do not marry? If so, where in the bible does it say that having a concubine (and obviously having sex with her) is a sin?
In particular, is it a sin to have sex with a woman whose marriage is not recognized by the state. So you have sex with her but you don't bother to apply for marriage license and do not agree to be bound by any rules governing civil marriage.
My questions is not a duplicate of Why was having concubines not a sin like adultery?
That question already assumes that having concubines is not a sin. This question asks if christian denominations think it is sin at all.
Also the highest voted answer in this question The Bible seems to allow polygamy. Why doesn't the church? says that polygamy is a sin because it's illegal and christians should obey the law. Cool. Polygamy is a sin. So why not have concubines instead, if it's not a sin? Having multiple wives is illegal. Having multiple concubines isn't.