SB 3.12.35
catur-hotram karma-tantram
upaveda-nayaih saha
dharmasya padas catvaras
tathaivasrama-vrttayah
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The four kinds of paraphernalia for conducting the fire sacrifice became manifest: the performer [the chanter], the offerer, the fire, and the action performed in terms of the supplementary Vedas. Also the four principles of religiosity [truth, austerity, mercy and cleanliness] and the duties in the four social orders all became manifest.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Eating, sleeping, defending and mating are the four principles of material bodily demands which are common to both the animals and human society. To distinguish human society from the animals there is the performance of religious activities in terms of the social statuses and orders of life. They are all clearly mentioned in the Vedic literatures and were manifested by Brahma when the four Vedas were generated from his four mouths. Thus the duties of humankind in terms of the statuses and social orders were established to be observed by the civilized man. Those who traditionally follow these principles are called Aryans, or progressive human beings.