Srimad Bhagavatam Canto 12, Chapter 04, Text 05

SB 12.4.5

dvi-parardhe tv atikrante
 brahmanah paramesthinah
tada prakrtayah sapta
 kalpante pralayaya vai
 
Translation: 
 
When the two halves of the lifetime of Lord Brahma, the most elevated created being, are complete, the seven basic elements of creation are annihilated.
Srimad Bhagavatam Canto 12, Chapter 04, Text 04
Srimad Bhagavatam Canto 12, Chapter 04, Text 06