Khandogya-Upanishad: Fourth Prapathaka, Fourteenth Khanda

2. 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?”

3. He answered: “This” (repeating some of what they had told him).

The teacher said: “My friend, they have taught you about the worlds, but I shall tell you this; and as water does not cling to a lotus leaf, so no evil deed clings to one who knows it.” He said: “Sir, tell it me.”