Ammar bin Abi Ammar narrates: We were sitting with Sayyiduna Ibn Abbas (may Allah be pleased with them both) at the funeral of Zayd bin Thabit (may Allah be pleased with him), and he said: "Today a great deal of knowledge has been buried."
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 4732