The Great Epic of the Bhārata dynasty 3.177.33

3.177.33

sarpa uvāca |
śrutaṃ viditavedyasya tava vākyaṃ yudhiṣṭhira |
bhakṣayeyamahaṃ kasmādbhrātaraṃ te vṛkodaram || 33 ||

"Yudhishthira said, 'In human society, O mighty and highly intelligent serpent, it is difficult to ascertain one's caste, because of promiscuous intercourse among the four orders. This is my opinion. Men belonging to all orders (promiscuously) beget offspring upon women of all the orders. And of men, speech, sexual intercourse, birth and death are common. And to this the Rishis have borne testimony by using as the beginning of a sacrifice such expressions as--of what caste so ever we may be, we celebrate the sacrifice. Therefore, those that are wise have asserted that character is the chief essential requisite. The natal ceremony of a person is performed before division of the umbilical cord. His mother then acts as its Savitri and his father officiates as priest. He is considered as a Sudra as long as he is not initiated in the Vedas. Doubts having arisen on this point, O prince; of serpents, Swayambhuba Manu has declared, that the mixed castes are to be regarded as better than the (other) classes, if having gone through the ceremonies of purification, the latter do not conform to the rules of good conduct, O excellent snake! Whosoever now conforms to the rules of pure and virtuous conduct, him have I, ere now, designated as a Brahmana.' The serpent replied, 'O Yudhishthira, thou art acquainted with all that is fit to be known and having listened to thy words, how can I (now) eat up thy brother Vrikodara!"