Srimad-Bhagavatam: Canto 11 - Chapter 1 - Verse 20
Sanskrit:
श्रीकरभाजन उवाचकृतं त्रेता द्वापरं च कलिरित्येषु केशव: ।नानावर्णाभिधाकारो नानैव विधिनेज्यते ॥ २० ॥
ITRANS:
śrī-karabhājana uvācakṛtaṁ tretā dvāparaṁ cakalir ity eṣu keśavaḥnānā-varṇābhidhākāronānaiva vidhinejyate
Translation:
Śrī Karabhājana replied: In each of the four yugas, or ages — Kṛta, Tretā, Dvāpara and Kali — Lord Keśava appears with various complexions, names and forms and is thus worshiped by various processes.