O most intelligent one, when the conditioned souls are devoted to their duties but have ulterior motives and seek personal prestige, you should understand such a situation to be the age of Tretā, in which the functions of passion are prominent.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
यदा धर्मार्थकामेषु भक्तिर्भवति देहिनाम् । तदा त्रेता रजो वृत्तिरिति जानीहि बुद्धिमन्
yadā dharmārthakāmeṣu bhaktirbhavati dehinām | tadā tretā rajo vṛttiriti jānīhi buddhiman
SB 12.3.28