bahir abrahmano dinam
tavaty eva nisa tata
yan nimilati visva-srk
tri-lokyah--of the three worlds; yuga--the four yugas; sahasram--one thousand; bahih--outside of; abrahmanah--up to Brahmaloka; dinam--is a day; tavati--a similar (period); eva--certainly; nisa--is night; tata--O dear one; yat--because; nimilati--goes to sleep; visva-srk--Brahma.
Outside of the three planetary systems [Svarga, Martya and Patala], the four yugas multiplied by one thousand comprise one day on the planet of Brahma. A similar period comprises a night of Brahma, in which the creator of the universe goes to sleep.
When Brahma goes to sleep in his nighttime, the three planetary systems below Brahmaloka are all submerged in the water of devastation. In his sleeping condition, Brahma dreams about the Garbhodakasayi Visnu and takes instruction from the Lord for the rehabilitation of the devastated area of space.