The Prophet ﷺ said, "Every division of inheritance made during the Days of Ignorance stands as it was divided, but every division reached by Islam follows the division of Islam."
قال النبي ﷺ: كل قسم قسم في الجاهلية فهو على ما قسم، وكل قسم أدركه الإسلام فهو على قسم الإسلام.
Abu Dawud (2914) and Ibn Majah (2485) both narrated it through the hadith of Musa bin Dawud, who said, Muhammad bin Muslim Taifi told us, from Amr bin Dinar, from Abu Shatha, from Ibn Abbas, and he related it. Its chain is hasan because of Muhammad bin Muslim Taifi, for he is hasan al-hadith, and he is among the men of Muslim. Through this same route it was also narrated by Tahawi in his Mushkil (3221), and Bayhaqi (9/122).Malik narrated it in the Aqdiya (37) as a balagh from Thawr bin Zayd Deeli, who said, it has reached me that the Messenger of Allah ﷺ said, "Whatever house or land was divided in the pre-Islamic era belongs according to the pre-Islamic division, and whatever house or land was reached by Islam without having been divided belongs according to the Islamic division."Bayhaqi (9/122) connected it by mentioning Ikrima, from Ibn Abbas, saying, Abu Abdullah informed us, Muhammad bin Muzaffar Hafiz told me, Abu Bakr bin Abu Dawud told us, Ahmad bin Hafs told us, my father told me, Ibrahim bin Tahman told us, from Malik, from Thawr bin Zayd, from Ikrima, from Ibn Abbas, who said, the Messenger of Allah ﷺ said, and he related the hadith.As for what was reported from Abdullah bin Umar in a similar raised form, it is daif. Ibn Majah (2749) narrated it from Muhammad bin Rumh, who said, Abdullah bin Lahia informed us, from Aqeel, that he heard Nafi relating from Abdullah bin Umar, and he related it. Abdullah bin Lahia has well known criticism against him, and Aqeel is Ibn Khalid Ayli, who is among the men accepted by the whole community.