Someone asked me a very confusing question. That if any husband and wife are agree to have intercourse with other husband and wife with each other at the same time in the same room, is it halal in Islam or not? Please shed some light on this issue if anyone knows about this. I already told him it's haram but I don't have any proof.
The proof is crystal clear in the qur'an:
And they who guard their private parts (5)
Except from their wives or those their right hands possess, for indeed, they will not be blamed - (6) But whoever seeks beyond that, then those are the transgressors - (23:5-7)
And those who guard their private parts (29) Except from their wives or those their right hands possess, for indeed, they are not to be blamed - (30) But whoever seeks beyond that, then they are the transgressors - (70:29-31)
So who ever gets intimate or had intercourse with a woman, which he didn't marry (in first place), is committing zina and Allah tells us:
And do not approach unlawful sexual intercourse. Indeed, it is ever an immorality and is evil as a way. (17:23)
Beyond this if a husband asks his wife to do this she is allowed to disobey as Allah says -protecting slave girls!-:
... And do not compel your slave girls to prostitution, if they desire chastity, to seek [thereby] the temporary interests of worldly life. And if someone should compel them, then indeed, Allah is [to them], after their compulsion, Forgiving and Merciful. (24:33)
So protecting married (free) woman should have at least the same level of imporance in Islam.
Finally note that a man is not even allowed to have sex with two of his wives at once in one bed (not mentioning the case of a foreign woman and man sharing it with him and his wife) (See for example: Is a Muslim husband allowed to have sex with his multiple wives simultaneously?). Because Islam has put boundaries to keep us clean and pure these are the rules of mahram-ship which order us to dress differently accoridng different cases like being alone with our spouses or with mahrams or with foreign people and anybody who is not a mahram is considered a foreigner.