SB 4.1.16
vidura uvaca
atrer grhe sura-sresthah
sthity-utpatty-anta-hetavah
kiñcic cikirsavo jata
etad akhyahi me guro
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
After hearing this, Vidura inquired from Maitreya: My dear master, how is it that the three deities Brahma, Visnu and Siva, who are the creator, maintainer and destroyer of the whole creation, became the offspring of the wife of Atri Muni?
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The inquisitiveness of Vidura was quite fitting, for he understood that when the Supersoul, Lord Brahma and Lord Siva all appeared through the person of Anasuya, the wife of Atri Muni, there must have been some great purpose. Otherwise why should they have appeared in such a way?