In the 2nd half of the 3rd Sandhi of Ādiparva, Vaiśampāyana narrates the story of Karṇa’s birth. One day Ṛṣi Durvāsa visited the kingdom of King Kuntibhōja. However as the king was busy with the affairs of the kingdom, he did not receive the esteemed Ṛṣi with due honours. Enraged by this, Durvāsa was about to curse King Kuntibhōja, when Kuntibhōja’s adopted daughter Kunti fell at the Ṛṣi’s feet and asked for forgiveness. Then Kunti took Durvāsa into her own palace and treated him with due honours, serving him various kinds of food and drinks. Extremely pleased by the young lady’s hospitality, Durvāsa taught her five mantra’s with which she could invoke any of the Deva-s she wished, and obtain sons from them.

Once Durvāsa left, out of curiosity, Kunti bathed in the waters of Gaṅgā and wearing a red coloured garment, she uttered the syllables of the mantra with great piety, all the while looking at the Sun. Sūryadeva, the Sun God, immediately descended on to the earth, and blessed her with a baby-boy. Looking at the beautiful radiant child in her arms, Kunti was awestruck. Overjoyed and thrilled by the fact that the mantra works, she hugged the child tightly. But then, it dawned on her that now she has a child out of wedlock. This will besmirch her family’s good name. Thus, concerted about the what people would say, Kunti put the child in a basket and floated it on the waters of Gaṅgā.
The child reached the other shore of Gaṅgā where it was found by a charioteer named Adhiratha, who waited to see if the child’s mother would come and pick it up. Seeing no one, the childless Adhiratha took the child home, and gave it to his wife Rādhā. He celebrated the arrival of his child with great pomp and joy. He named the child Rādheya, after his wife. The news about a radiant child in Adhiratha’s house fell into the people’s ears. Thus, through word-of-mouth, his name spread throughout the world. But that was not the name that Adhiratha gave him. The Deva-s, the Nāga-s, the Men, would all call him by the name Karṇa. This brave warrior was growing up in the house of the charioteer.

Audio Link : https://archive.org/download/kumaravyasa-bharata-recitation/Parva-01-Adiparva-003-Sandhi-Part-02-of-02.mp3