Ibn Abi al-Zinad (may Allah have mercy on him) narrates from the jurists of the people of Madinah that they used to say: Any people who would inherit from one another and who die, whether from something collapsing on them, by drowning, by burning or from any other cause, and it is not known whose death came before the other's, neither inherit from one another nor exclude (others) as hajib (blockers). This was the view of Zayd bin Thabit (may Allah be pleased with him), and Umar bin Abd al-Aziz (may Allah have mercy on him) ruled accordingly.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الفرائض / 12253