The Great Epic of the Bhārata dynasty 3.177.23

3.177.23

evametanmataṃ sarpa tābhyāṃ hīnaṃ na vidyate |
yathā śītoṣṇayormadhye bhavennoṣṇaṃ na śītatā || 23 ||

"Yudhishthira said, Those characteristics that are present in a Sudra, do not exist in a Brahmana; nor do those that are in a Brahmana exist in a Sudra. And a Sudra is not a Sudra by birth alone--nor a Brahmana is Brahmana by birth alone. He, it is said by the wise, in whom are seen those virtues is a Brahmana. And people term him a Sudra in whom those qualities do not exist, even though he be a Brahmana by birth. And again, as for thy assertion that the object to be known (as asserted by me) doth not exist, because nothing exists that is devoid of both (happiness and misery), such indeed is the opinion, O serpent, that nothing exists that is without (them) both. But as in cold, heat doth not exist, nor in heat, cold, so there cannot exist an object in which both (happiness and misery) cannot exist?"