From Chhandogya Upanishad (7.1-3) in Swami Nikhilananda’s translation:
Narada approached Sanatkumara [as a pupil] and said: “Venerable Sir, please teach me.”
Sanatkumara said to him: “Please tell me what you already know. Then I shall tell you what is beyond.”
Narada said: “Venerable Sir, I know the Rig-Veda, the Yajur-Veda, the Sama-Veda, the Atharva-Veda as the fourth, the epics and ancient lore as the fifth, the Veda of the Vedas (i.e. grammar), the rules of the sacrifices by which the Manes are gratified, the science of numbers, the science of portents, the science of time, logic, ethics, etymology, Brahma-vidya (i.e. the science of pronunciation, ceremonials, prosody, etc.), the science of elemental spirits, the science of weapons, astronomy, the science of serpents, and the fine arts. All that I know, Venerable Sir.
“But, venerable Sir, with all that I know world only; I do not know the Self. I have heard from men like you that he who knows the Self overcomes sorrow. I am on afflicted with sorrow. Do you, venerable Sir, help me to cross over the the other side of sorrow.”
Sanatkumara said to him: “Whatever you have read is only a name.”