SB 12.3.28

yadā karmasu kāmyeṣu
 bhaktir yaśasi dehinām
tadā tretā rajo-vṛttir
 iti jānīhi buddhiman
Synonyms: 
yadā — when; karmasu — in duties; kāmyeṣu — based on selfish desire; bhaktiḥ — devotion; yaśasi — in honor; dehinām — of the embodied souls; tadā — then; tretā — the age of Tretā; rajaḥ-vṛttiḥ — predominated by activities in the mode of passion; iti — thus; jānīhi — you should understand; buddhi-man — O intelligent King Parīkṣit.
Translation: 
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.