Srimad-Bhagavatam: Canto 1 - Chapter 1 - Verse 1
सूत उवाचविदुरस्तीर्थयात्रायां मैत्रेयादात्मनो गतिम् ।ज्ञात्वागाद्धास्तिनपुरं तयावाप्तविवित्सित: ॥ १ ॥
sūta uvācaviduras tīrtha-yātrāyāṁmaitreyād ātmano gatimjñātvāgād dhāstinapuraṁtayāvāpta-vivitsitaḥ
Śrī Sūta Gosvāmī said: While traveling on a pilgrimage, Vidura received knowledge of the destination of the self from the great sage Maitreya and then returned to Hastināpura. He became as well versed in the subject as he desired.
Vidura: One of the prominent figures in the history of the Mahābhārata. He was conceived by Vyāsadeva in the womb of the maidservant of Ambikā, mother of Mahārāja Pāṇḍu. He is the incarnation of Yamarāja. Being cursed by Maṇḍūka Muni, he was to become a śūdra. The story is narrated as follows: Once upon a time the state police caught some thieves who had concealed themselves in the hermitage of Maṇḍūka Muni. The police constables, as usual, arrested all the thieves and Maṇḍūka Muni along with them. The magistrate specifically punished the muni to death by being pierced with a lance. When he was just to be pierced, the news reached the king, and he at once stopped the act on consideration of his being a great muni. The king personally begged the muni’s pardon for the mistake of his men, and the saint at once went to Yamarāja, who prescribes the destiny of the living beings. Yamarāja, being questioned by the muni, replied that the muni in his childhood pierced an ant with a sharpened straw, and for that reason he was put into difficulty. The muni thought it unwise on the part of Yamarāja that he was punished for his childish innocence, and thus the muni cursed Yamarāja to become a śūdra, and this śūdra incarnation of Yamarāja was known as Vidura, the śūdra brother of Dhṛtarāṣṭra and Mahārāja Pāṇḍu. But this śūdra son of the Kuru dynasty was equally treated by Bhīṣmadeva, along with his other nephews, and in due course Vidura was married with a girl who was also born in the womb of a śūdrāṇī by a brāhmaṇa. Although Vidura did not inherit the property of his father (the brother of Bhīṣmadeva), still he was given sufficient state property by Dhṛtarāṣṭra, the elder brother of Vidura. Vidura was very much attached to his elder brother, and all along he tried to guide him on the right path. During the fratricidal war of Kurukṣetra, Vidura repeatedly implored his elder brother to do justice to the sons of Pāṇḍu, but Duryodhana did not like such interference by his uncle, and thus he practically insulted Vidura. This resulted in Vidura’s leaving home for pilgrimage and taking instructions from Maitreya.