I know that you are now Vidura due to the cursing of Māṇḍavya Muni and that formerly you were King Yamarāja, the great controller of living entities after their death. You were begotten by the son of Satyavatī, Vyāsadeva, in the kept wife of his brother.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
माण्डव्यशापाद्भगवान् प्रजासंयमनो यमः । भ्रातुः क्षेत्रे भुजिष्यायां जातः सत्यवतीसुतात्
māṇḍavyaśāpādbhagavān prajāsaṃyamano yamaḥ | bhrātuḥ kṣetre bhujiṣyāyāṃ jātaḥ satyavatīsutāt
SB 3.5.20