" And if a woman has reason to fear ill-treatment from her husband or that he might turn away from her" that it was revealed in case of a woman who lived with a person and perhaps he does not want to prolong (his relationship with her) whereas she has had sexual relationship with him (and as a result thereof) she got a child from him and she does not like that she should be divorced, so she says to him: I permit you to live with the other wife.  

عَنْ عَائِشَةَ فِي قَوْلِهِ ﷻ { وَإِنِ امْرَأَةٌ خَافَتْ مِنْ بَعْلِهَا نُشُوزًا أَوْ إِعْرَاضًا} قَالَتْ نَزَلَتْ فِي الْمَرْأَةِ تَكُونُ عِنْدَ الرَّجُلِ فَلَعَلَّهُ أَنْ لاَ يَسْتَكْثِرَ مِنْهَا وَتَكُونُ لَهَا صُحْبَةٌ وَوَلَدٌ فَتَكْرَهُ أَنْ يُفَارِقَهَا فَتَقُولُ لَهُ أَنْتَ فِي حِلٍّ مِنْ شَأْنِي  

regarding the Verse: 'If a wife fears cruelty or desertion on her husband's part ...') (4.128) It concerns the woman whose husband does not want to keep her with him any longer, but wants to divorce her and marry some other lady, so she says to him: 'Keep me and do not divorce me, and then marry another woman, and you may neither spend on me, nor sleep with me.' This is indicated by the Statement of Allah: 'There is no blame on them if they arrange an amicable settlement between them both, and (such) settlement is better." (4.128) (Using translation from Bukhārī 5206)   

عَنْ عَائِشَةَ فِي قَوْلِهِ تَعَالَى {وَإِنِ امْرَأَةٌ خَافَتْ مِنْ بَعْلِهَا نُشُوزًا أَوْ إِعْرَاضًا} [النساء 128] أُنْزِلَتْ فِي الْمَرْأَةِ تَكُونُ عِنْدَ الرَّجُلِ لَا يَسْتَكْثِرُ مِنْهَا فَيُرِيدُ أَنْ يُطَلِّقَهَا وَيَتَزَوَّجَ غَيْرَهَا فَتَقُولُ لَا تُطَلِّقْنِي وَأَمْسِكْنِي وَأَنْتَ فِي حِلٍّ مِنَ النَّفَقَةِ وَالْقِسْمَةِ لِي فَأَنْزَلَ اللهُ جَلَّ وَعَزَّ {فَلَا جُنَاحَ عَلَيْهِمَا أَنْ يُصْلِحَا بَيْنَهُمَا صُلْحًا} [النساء 128]  

[Machine] In His statement {And if a woman fears from her husband contempt or evasion} [An-Nisa: 128], it is said that this verse was revealed regarding a woman who her husband does not show favor towards her and wishes to divorce her and marry someone else. So, she says, "Do not divorce me, keep me in a state of marriage while you are capable of providing for me and fulfilling the obligations towards me." Then Allah, may He be glorified and exalted, revealed {There is no blame upon them if they make terms of settlement between themselves} [An-Nisa: 128].  

ؓ فِي قَوْلِهِ {وَإِنِ امْرَأَةٌ خَافَتْ مِنْ بَعْلِهَا نُشُوزًا أَوْ إِعْرَاضًا} [النساء 128] قَالَتْ نَزَلَتْ فِي الْمَرْأَةِ تَكُونُ عِنْدَ الرَّجُلِ لَا يَسْتَكْثِرُ مِنْهَا فَيُرِيدُ أَنْ يُطَلِّقَهَا وَيَتَزَوَّجَ غَيْرَهَا فَتَقُولُ لَا تُطَلِّقْنِي وَأَمْسِكْنِي وَأَنْتَ فِي حِلٍّ مِنَ النَّفَقَةِ وَالْقِسْمَةِ لِي فَأَنْزَلَ اللهُ ﷻ {لَا جُنَاحَ عَلَيْهِمَا أَنْ يُصْلِحَا بَيْنَهُمَا صُلْحًا} الْآيَةَ