This doctrine (beginning with III, 1, 1) Brahman (m. Hiranyagarbha) told to Pragâpati (Virâg), Pragâpati to Manu, Manu to his offspring (Ikshvâku, &c.) And the father told that (doctrine of) Brahman (n.) to Uddâlaka Âruni.

In plain words: This teaching was handed down from the creator god to Prajapati, then to Manu the first man, then to his descendants. Finally, a father passed it on to the sage Uddalaka Aruni.