Abu Ubayd (may Allah have mercy on him) says concerning the hadith of Ibn Abbas (may Allah be pleased with them both), about a man who had four wives and divorced one of them, not knowing which one he had divorced, that he said: 'Yanaluhunna min al-talaq ma yanaluhunna min al-mirath' (Of divorce, they get what they get of inheritance). That is, if the man dies having divorced one wife without it being known which one she was, the inheritance will go to all of them until the divorced wife is identified; or else he will separate from all of them if the divorce was three.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الخلع والطلاق / 15134