I don’t recall something like that happening at the time of the Prophet salla Allahu alaihi wa sallam .

However, there is a difference between separation enforced by the Judge and Khul’a.

If there is proven harm on the wife, the judge has the right to grant her divorce and separation from her husband without any financial implications on her side.

Did it ever happen in the life of the Prophet peace and blessings be upon him or in the time of the khulafa e ,rashedeen, that a woman took khula on grounds of oppression and cruelty after several years of marriage and having had a child. And was allowed not to return mehr by the Islamic judge, because of the cruelty involved. Or is mehr always returned, no matter how justifiable the reason for khula?