Razin al-Jurjani (may Allah have mercy on him) said: I asked Sa'id bin Jubayr (may Allah have mercy on him) about this verse, "And [also forbidden to you are] married women", and he said: "I have no knowledge of it." Then I asked al-Dahhak bin Muzahim (may Allah have mercy on him) and mentioned to him what Sa'id bin Jubayr (may Allah have mercy on him) had said, and he said: "I bear witness that I heard Sa'id asking Sayyiduna Ibn Abbas (may Allah be pleased with them both) about it, and Ibn Abbas (may Allah be pleased with them both) said that this verse was revealed on the occasion of Khaybar. When the Messenger of Allah (peace and blessings be upon him) conquered Khaybar, some women of the People of the Book, who had husbands (living), fell into the hands of the Muslims, and whenever a man intended to go to one of these women, she would say: 'I have a husband.' So the Messenger of Allah (peace and blessings be upon him) was asked about that, and this verse was revealed: 'And [also forbidden to you are] married women' (to the end of the verse), meaning: there is no harm in having relations with the women of the polytheists who come as captives."
Then I mentioned this to Sa'id bin Jubayr (may Allah have mercy on him), and he said: "Al-Dahhak has spoken the truth."
Imam al-Tabarani (may Allah have mercy on him) said: "No one narrated it from Salim al-Aftas except Muhammad bin Muslim bin Abi al-Waddah."
Hadith Referenceالمعجم الأوسط / باب العين / 4251
Hadith Takhrij«أخرجه البيهقي فى «السنن الكبرى» برقم: 14088، 14087، والطبراني فى «الكبير» برقم: 12607، 12637»