Praise be to Allah.
If a man says to his wife: “If you want So and so, take him, and let his wife take your place”, that does not count as a divorce or separation, because it does not contain any of the words of talaaq or metaphors thereof, and it does not make his wife haraam for him. It is also conditional on whether the wife wants that. Such words do not count as divorce.
However we think that this is not appropriate, and it comes under the heading of slips of the tongue that may lead a man to doom, because it is taking sacred limits lightly and is a verbal transgression against the Muslims’ honour, and it is taking away the sense of protective jealousy that protects Muslim families from immorality. Can it be proper or dignified for a Muslim to suggest to his wife that she be married to some other man and share his bed, even if in return for that he will take the wife of the other man? What justification can there be for a man to allow himself to say that and talk about that man and his wife in that manner, when talking and joking with his wife??
Honourable and kind treatment dictates that each spouse should be pleased with the other, and should know for certain that what the Shaytaan makes him think of a happy life with another spouse is merely foolish notions, as Allah, may He be glorified and exalted, says ( interpretation of the meaning):
“And whoever takes Shaytaan (Satan) as a Walee (protector or helper) instead of Allah, has surely suffered a manifest loss.
He (Shaytaan (Satan)) makes promises to them, and arouses in them false desires; and Shaytaan’s (Satan’s) promises are nothing but deceptions” [an-Nisa’ 4:119-120].
Similarly, exchanges of hurtful words between spouses may reach the level of sin, or seeking to commit immoral deeds, whether that occurs by way of joking or in earnest, and sometimes it may be a cause of arguments and disputes that lead to separation. The wise man is the one who closes the door to the Shaytaan and protects himself and his family from all kinds of evil by doing one easy thing, of which the Prophet (blessings and peace of Allah be upon him) told us when he said: “Restrain your tongue, be content in your house, and weep for your sin.” Narrated by at-Tirmidhi in as-Sunan (2406); he said: A hasan hadith. It was classed as saheeh by al-Albaani in Saheeh at-Tirmidhi.
We have heard from one of the righteous people of our times that he said: I have been married for fifty years, and I never joked with my wife about taking a second wife, for fear that it would break her heart.
So a man should fear his Lord lest he says something that is not appropriate, or lest his jokes go beyond the limit of what is reasonable and permissible to that which is inappropriate and hurtful, and causes trouble, and he ends up regretting it one day, at a time when regret will not benefit him.
And Allah knows best.