Sawdah feared that the Prophet ﷺ might divorce her, so she said, "Do not divorce me. Keep me as your wife and give my day to Ayesha." He did so, and the verse was revealed, "There is no blame on them if they make a settlement between themselves, and settlement is best" [Nisa 4:128]. So whatever they agree upon as a settlement is permissible. This appears to be the statement of Ibn Abbas.
حدثنا محمد بن المثنى حدثنا أبو داود حدثنا سليمان بن معاذ عن سماك عن عكرمة
خشيت سودة أن يطلقها النبي ﷺ فقالت لا تطلقني وأمسكني واجعل يومي لعائشة ففعل فنزلت {فلا جناح عليهما أن يصلحا بينهما صلحا والصلح خير} فما اصطلحا عليه من شيء فهو جائز كأنه من قول ابن عباس
[Sahih]. Bayhaqi related it, 7/297, from the hadith of Abu Dawud Tayalisi, through him, and it is found in Musnad Abu Dawud Tayalisi, no. 2683, though its chain is daif. The hadith has many corroborating witnesses in Bukhari, no. 5067, Muslim, no. 1463 and 1465, Nasai, no. 3199, and others.