Vishnupurana 4.14.9

4.14.9

śūrasya kuntir nāma sakhābhavat |
tasmai cāputrāya pṛthām ātmajāṃ vidhinā śūro dattavān |
tāṃ ca pāṇḍur uvāha |
tasyāṃ ca dharmānilaśakrair yudhiṣṭhirabhīmārjunākhyās trayaḥ putrāḥ samutpāditāḥ |
pūrvam anūḍhāyāś ca bhagavatā bhāsvatā kānīnaḥ karṇo nāma putro 'janyata ||

Śúra had a friend named Kuntibhoja, to whom, as he had no children, the presented in due form his daughter Pritha. She was married to Pańd́u, and bore him Yudhisht́hira, Bhíma, and Arjuna, who were in fact the sons of the deities Dharma, Váyu (air), and Indra. Whilst she was yet unmarried, also, she had a son named Karńa, begotten by the divine Áditya (the sun). Pańd́u had another wife, named Mádrí, who had by the twin sons of Áditya, Násatya and Dasra, two sons, Nakula and Sahadeva.