It is reported from him that he said: "Do you know what the departure of knowledge means? It is the departure of the scholars from the earth."
Ahmad recorded it within a hadith that will come later in the chapter on Surah Sa'ala; its chain contains a narrator, Qabus, about whom there is disagreement over whether he can be used as evidence. The hadith narrated from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) will come later in the chapter on the shares of inheritance (fara'id).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب العلم / 992