Brihadaranyaka-Upanishad: Third Adhyya, Fifth Brahmana
1.Then Kahola Kaushitakeya asked. ?Yagnavalkya,? he said, ?tell me the Brahman which is visible, not invisible, the Self (atman), who is within all.?
Yagnavalkya replied: ?This, thy Self, who is within all.?
?Which Self, O Yagnavalkya, is within all??
Yagnavalkya replied: ?He who overcomes hunger and thirst, sorrow, passion, old age, and death. When Brahmanas know that Self, and have risen above the desire for sons, wealth, and (new) worlds, they wander about as mendicants. For a desire for sons is desire for wealth, a desire for wealth is desire for worlds. Both these are indeed desires. Therefore let a Brahmana, after he has done with learning, wish to stand by real strength; after he has done with that strength and learning, he becomes a Muni (a Yogin); and after he has done with what is not the knowledge of a Muni, and with what is the knowledge of a Muni, he is a Brahmana. By whatever means he has become a Brahmana, he is such indeed. Everything else is of evil.? After that Kahola Kaushitakeya held his peace.