Chandogya Upanishad
Prapathaka IV, Khanda 9
Thus he reached the house of his teacher. The teacher said to him: 'Satyakâma.' He replied: 'Sir.'
The teacher said: 'Friend, you shine like one who knows Brahman. Who then has taught you ?' He replied: 'Not men. But you only, Sir, I wish, should teach me ;