Ammar bin Abi Ammar (may Allah have mercy on him) said: When Zayd bin Thabit (may Allah be pleased with him) died, we were sitting with Abdullah bin Abbas (may Allah be pleased with him) in the shade of a building, and he said: This is how knowledge departs; indeed, a great deal of knowledge has been buried today.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الفرائض / 12197