What is the ruling on an agreement between a divorced man and his ex-wife and her guardian to annul her marriage to her second husband so that he (the ex-husband) may marry her again, due to the presence of children and the wife's desire?

A woman is permitted to seek khul' (divorce at the wife's instance, usually with compensation) from her husband if she dislikes him and fears she will not be able to fulfill God's rights with him. However, khul' is not permissible without a valid reason, as the Prophet, peace and blessings be upon him, said: "Women who seek khul' are the hypocrites." If a woman is harmed by remaining with her husband, it is permissible for someone else to agree with the husband to seek khul' on her behalf to alleviate her harm, such as a third party saying to the husband, "Divorce your wife for a thousand from me," provided the intention is solely to free her for her own benefit. As for a man inciting a woman to seek khul' so that he can marry her, this is impermissible and a major sin, as the Prophet, peace and blessings be upon him, said: "He is not of us who incites a woman against her husband or a slave against his master." Some scholars have even ruled that the marriage of a woman to the one who incited her against her husband is null and void, and they must be separated.