When the mind, intelligence and senses are solidly fixed in the mode of goodness, that time should be understood as Satya-yuga, the age of truth. People then take pleasure in knowledge and austerity.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
प्रभवन्ति यदा सत्त्वे मनोबुद्धीन्द्रियाणि च । तदा कृतयुगं विद्याज्ज्ञाने तपसि यद्रुचिः
prabhavanti yadā sattve manobuddhīndriyāṇi ca | tadā kṛtayugaṃ vidyājjñāne tapasi yadruciḥ
SB 12.3.27