“(Rishi) Shaunaka said, ‘O child (Soota), you have named many snakes gifted with great energy and incapable of being easily overcome. What did they do after hearing of that curse (of their mother Kadru)?’
“Soota said, ‘The illustrious (Aadi) Sesha among them, of great fame, leaving his mother practiced hard Tapas, living upon air and rigidly observing his vows (Vrata in Sanskrit). He practised these severe Tapas, travelling to Gandhamaadana (Mountain Gandhamaadana is located near mount Kailash), Badri (present day Badrinath, Chamoli district, Uttarakhand, India), Gokarna (present day Gokarna, Uttara Kannada district, Karnataka, India), the forest of Pushkara (possibly present day Pushkar in the Ajmer district, Rajasthan, India), and the foot of Himavat (Himalayas).
“He passed his days in those sacred regions, some of which were sacred for their water and others for their soil in the rigid observance of his vows, with singleness of aim, and his passions under complete control. The Pitaamaha of all, (Lord) Brahma, saw that (Aadi) Sesha with knotted hair, dressed in rags, his flesh, skin, and muscles dried up owing to the hard penances he was practicing. The Pitaamaha addressing him, that penance-practicing one of great courage (Aadi Sesha snake), said, ‘What is that you are doing, O Sesha? Let the welfare of the creatures of the worlds also engage your thoughts. O sinless one, you are creating pain on all creatures by your hard Tapas. O Sesha, tell me the desire implanted in your heart.’
“Sesha replied, ‘My blood brothers (other snakes) are all of wicked hearts. I do not desire to live among them. Let this be sanctioned by You. Like enemies, they are always jealous of one another. I am, therefore, engaged in Tapas. I will not see them even. They never show any kindness for Vinata (Garuda’s mother) and her son. Indeed, Vinata’s son capable of travelling through the skies, is another brother of ours. They always envy him. He, too, is much stronger owing to the bestowal of that boon by our father, the Mahatma Kashyapa. For these, I engaged in Tapas, and I will cast off this body of mine, so that I may avoid companionship with them, even in another state of life.’
“To Sesha who had said so, the Pitaamaha (Lord Brahma) said, ‘O Sesha, I know the behavior of all your brothers and their great danger owing to their offence against their mother. But O Snake, a remedy (for this) has been provided by me even beforehand. It is your duty not to grieve for your brothers. O Sesha, ask of me the boon you desire. I have been highly pleased with you and I will grant you today a boon. O best of snakes, it is fortunate that your heart has been set on Dharma. Let your heart be more and more firmly set on Dharma.’
“Then Sesha replied, ‘O divine Pitaamaha (Lord Brahma), this is the boon desired by me; viz., may my heart always delight in Dharma and in blessed Tapas, O Lord of all!’
“(Lord) Brahma said, ‘O Sesha, I am exceedingly pleased with this your self-denial and love of peace. But, at my command, let this act be done by you for the good of my creatures. You bear, O Sesha, properly and well this Earth so unsteady with her mountains and forests, her seas and towns and retreats, so that she may be steady.’
“Sesha said, ‘O divine Lord of all creatures (Lord Brahma), O bestower of boons, O lord of the Earth, lord of every created thing, lord of the Universe, I will, as you say hold the Earth steady. Therefore, O lord of all creatures, place her on my head.’
“(Lord) Brahma said, ‘O best of snakes, go below the Earth. She will herself give you a crack to pass through. O Sesha, by holding the Earth, you shall certainly do what is praised by me very greatly.’
“Soota continued, ‘Then the elder brother of the king of the snakes (Aadi Sesha), entering a hole, passed to the other side of the Earth, and holding her, supported with his head that goddess with her belt of seas passing all round.’
“(Lord) Brahma said, ‘O Sesha, O best of Naagaas, you are the Dharmadeva, because alone, with your huge body, you support the Earth with everything on her, as I myself, or Balabhit (Lord Indra), can.’
“Soota continued, ‘The snake, Sesha, the lord Ananta, of great skills, lives underneath the Earth, alone supporting the world at the command of (Lord) Brahma. The illustrious Pitaamaha (Lord Brahma), the best of the immortals, then gave to Ananta the friendship with the bird of fair feathers, viz., the son of Vinata (Vainateya in Sanskrit), for Ananta’s help.’”
SRIMAD MAHABHARATA – AADI PARVA – AASTIKA (UPA) PARVA – PART 36 – AADI SESHA BEARS THE EARTH