Vajrasuci (Siddhacarya Ghoshapada) 41

41

kiṃ ca bhūyo vaiśampāyanenoktam :
ekavarṇamidaṃ pūrvaṃ viśvamāsīd yudhiṣṭhira
karmakriyāviśeṣeṇa cāturvarṇyaṃ pratiṣṭhitam127

Moreover, it was further said by Vaiśampāyana:
Formerly, this entire world was of one class, O Yudhiṣṭhira;
through distinction in deeds and actions the system of four classes was established.