Srimad-Bhagavatam: Canto 4 - Chapter 1 - Verse 2
विदुर उवाचके ते प्रचेतसो नाम कस्यापत्यानिसुव्रत ।कस्यान्ववाये प्रख्याता: कुत्र वा सत्रमासत ॥ २ ॥
vidura uvācake te pracetaso nāmakasyāpatyāni suvratakasyānvavāye prakhyātāḥkutra vā satram āsata
Vidura inquired from Maitreya: O greatly advanced devotee, who were the Pracetās? To which family did they belong? Whose sons were they, and where did they perform the great sacrifices?
The great Nārada’s singing, in the previous chapter, of three verses in the sacrificial arena of the Pracetās gave another impetus to Vidura to ask further questions.