Mbh 12.346.4a

"'"Vrishakapi said, 'I and the Creator of the worlds. I am resolved to create those that are to be called Pitris.'--Saying these words, he began to think of those high ordinances that should regulate the rites to be gone through in honour of the Pitris. While thus engaged, he saw that the three balls of mud, shaken off his tusk, had fallen towards the South. He then said unto himself,--'These balls, shaken off my tusk, have fallen on the Earth towards the southern direction of her surface. Led by this, I declare that these should be known henceforth by the name of Pitris. Let these three that are of no particular shape, and that are only round, come to be regarded as Pitris in the world. Even thus do I create the eternal Pitris. I am the father, the grandfather, and the great grandfather, and I should be regarded as residing in these three Pindas. There is no one that is superior to me. Who is there whom I myself may worship or adore with rites? Who, again, is my sire in the universe? I myself am my grandfather. I am, indeed, the Grandsire and the Sire. I am the one cause (of all the universe).'--Having said these words, that God of gods, Vrishakapi by name, offered those Pindas, O learned Brahmana, on the breast of the Varaha mountains, with elaborate rites. By those rites He worshipped His own self, and having finished the worship, disappeared there and then. Hence have the Pitris come to be called by the name of Pinda. Even this is the foundation of the designation. Agreeably to the words uttered by Vrishakapi on that occasion, the Pitris receive the worship offered by all. They who perform sacrifices in honour of and adore the Pitris, the deities, the preceptor or other reverend senior guests arrived at the house, kine, superior Brahmanas, the goddess Earth, and their mothers, in thought, word, and deed, are said to adore and sacrifice unto Vishnu himself. Pervading the bodies of all existent creatures, the illustrious Lord is the Soul of all things.