Srimad-Bhagavatam: Canto 4 - Chapter 1 - Verse 16

Sanskrit:

विदुर उवाचअत्रेर्गृहे सुरश्रेष्ठा: स्थित्युत्पत्त्यन्तहेतव: ।किञ्चिच्चिकीर्षवो जाता एतदाख्याहि मे गुरो ॥ १६ ॥

ITRANS:

vidura uvācaatrer gṛhe sura-śreṣṭhāḥsthity-utpatty-anta-hetavaḥkiñcic cikīrṣavo jātāetad ākhyāhi me guro

Translation:

After hearing this, Vidura inquired from Maitreya: My dear master, how is it that the three deities Brahmā, Viṣṇu and Śiva, who are the creator, maintainer and destroyer of the whole creation, became the offspring of the wife of Atri Muni?

Purport:

The inquisitiveness of Vidura was quite fitting, for he understood that when the Supersoul, Lord Brahmā and Lord Śiva all appeared through the person of Anasūyā, the wife of Atri Muni, there must have been some great purpose. Otherwise why should they have appeared in such a way?