Bhagavatapurana 1.10.25

1.10.25

yadā hyadharmeṇa tamodhiyo nṛpā jīvanti tatraiṣa hi sattvataḥ kila /
dhatte bhagaṃ satyam ṛtaṃ dayāṃ yaśo bhavāya rūpāṇi dadhadyuge yuge //

25.* Whenever kings whose understanding is overpowered by Tamas, care only to maintain themselves by unrighteous ways, (then indeed) from age to age this Supreme Lord assumes several forms through Satva in order to sustain the world, and thereby promote prosperity, truthfulness, right knowledge and true precept, showing thus His mercifulness in His glorious activity.