Rabi' bin Sulayman (may Allah have mercy on him) says: I asked Imam al-Shafi'i (may Allah have mercy on him) about the people of a dwelling among the people of war (ahl al-harb) who divide the property among themselves, each owning his share by that division; then they accept Islam, and then one of them wants to undo that division and divide it according to the division of estates. He said: That is not his right. I asked for the proof, and he said: Inference from the meaning of consensus and the Sunnah, just as they are not held to account for killing one another, taking one another captive, or usurping one another's property. Thawr bin Zayd al-Dili (may Allah have mercy on him) says: It has reached me that the Messenger of Allah (peace and blessings be upon him) said: "Whatever house or land was divided in the Jahiliyyah remains upon that division of the Jahiliyyah, and whatever house or land Islam reached undivided will be divided according to the principles of Islam."
Al-Shafi'i said: We narrate on this matter a hadith more established than this, which has reached me with a similar meaning.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18285
Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) narrates from the Prophet (peace and blessings be upon him): "Every division that was made in the Jahiliyyah remains as it was, and every division that was made in accordance with Islamic principles will remain as it is."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18286
Ikrimah narrates from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said, and he mentioned it in the same way as the narration of Imam al-Shafi'i (may Allah have mercy on him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18287