SB 5.20.16
yasam payobhih kusadvipaukasah kusala-kovidabhiyukta-kulaka-samjña bhagavantam jataveda-sarupinam karma-kausalena yajante.
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The inhabitants of the island of Kusadvipa are celebrated as the Kusalas, Kovidas, Abhiyuktas and Kulakas. They are like the brahmanas, ksatriyas, vaisyas and sudras respectively. By bathing in the waters of those rivers, they all become purified. They are expert in performing ritualistic ceremonies according to the orders of the Vedic scriptures. Thus they worship the Lord in His aspect as the demigod of fire.