The most authoritative formulation is in the Manusmṛti. It remains the orthodox Hindu ideal, although it is seldom if ever followed exactly according to Manusmṛti.
"Varṇāśramadharma." The Concise Oxford Dictionary of World Religions. . Encyclopedia.com. (August 19, 2018). http://www.encyclopedia.com/religion/dictionaries-thesauruses-pictures-and-press-releases/varnasramadharma
"Varṇāśramadharma." The Concise Oxford Dictionary of World Religions. . Retrieved August 19, 2018 from Encyclopedia.com: http://www.encyclopedia.com/religion/dictionaries-thesauruses-pictures-and-press-releases/varnasramadharma