'A'isha said in connection with the verse:
" And if a woman has reason to fear ill-treatment from her husband or that he might turn away from her" (iv. 128) that it was revealed in case of a woman who had long association with a person (as his wife) and now he intends to divorce her and she says: Do not divorce me, but retain me (as wife in your house) and you are permitted to live with another wife. It is in this context that this verse was revealed.
Reference: Sahih Muslim 3021 a
In-book reference: Book 56, Hadith 15
USC-MSA web (English) reference(deprecated numbering scheme): Book 43, Hadith 7165