Śrīmad-Bhāgavatam · Text 11.17.10
Who is speaking and story frame
आदौ कृतयुगे वर्णो नृणां हंस इति स्मृत: ।
कृतकृत्या: प्रजा जात्या तस्मात् कृतयुगं विदु: ॥ १० ॥
ādau kṛta-yuge varṇo
nṛṇāṁ haṁsa iti smṛtaḥ
kṛta-kṛtyāḥ prajā jātyā
tasmāt kṛta-yugaṁ viduḥ
In the beginning, in Satya-yuga, there is only one social class, called haṁsa, to which all human beings belong. In that age all people are unalloyed devotees of the Lord from birth, and thus learned scholars call this first age Kṛta-yuga, or the age in which all religious duties are perfectly fulfilled.
Read the purport on Vedabase.ioFrom Canto 10, chapter 14 onward, the translation and purports were completed by Śrīla Prabhupāda's disciples after his departure, and published by the Bhaktivedanta Book Trust.