Srimad-Bhagavatam: Canto 3 - Chapter 1 - Verse 35


चातुर्होत्रं कर्मतन्त्रमुपवेदनयै: सह ।धर्मस्य पादाश्चत्वारस्तथैवाश्रमवृत्तय: ॥ ३५ ॥


cātur-hotraṁ karma-tantramupaveda-nayaiḥ sahadharmasya pādāś catvārastathaivāśrama-vṛttayaḥ


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.


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 Brahmā 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 Āryans, or progressive human beings.