Yusuf bin al-Majishun said: I heard Ibn Shihab (may Allah have mercy on him) saying: Had Uthman bin Affan and Zayd bin Thabit (may Allah be pleased with them both) died early, the science of fara'id (inheritance) would have perished until the Day of Resurrection. A time came upon the people when no one other than these two knew it well.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الفرائض / 12191