Srimad Bhagavatam Canto-02, Chapter-10, Text-46
ayam tu brahmanah kalpah
vidhih sadharano yatra
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
This process of creation and annihilation described in summary herein is the regulative principle during the duration of Brahma’s one day. It is also the regulative principle in the creation of mahat, in which the material nature is dispersed.
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