The Kalpas and Manvantaras: their duration - Verse 67

Sūta said: By means of the three (qualities or forms), he creates, devours and sees or protects (the world). In the vast sheet of water, when the mobile and the immobile beings have perished, at the end of a thousand sets of four Yugas, when (the earth) is covered on all sides with water, Brahmā named Nārāyaṇa shines himself in the universe.