Chandogya Upanishad
Prapathaka IV, Khanda 14
Then they all said: 'Upakosala, this is our knowledge, our friend, and the knowledge of the Self, but the teacher will tell you the way (to another life).'
In time his teacher came back, and said to him: 'Upakosala.' He answered: 'Sir.' The teacher said: 'Friend, your face shines like that of one who knows Brahman. Who has taught you?' 'Who should teach me, Sir?' he said. He denies, as it were. And he said (pointing) to the fires: 'Are these fires other than fires?' The teacher said: 'What, my friend, have these fires told you?'