Srimad Bhagavatam Canto 03, Chapter 12, Text 44

SB 3.12.44

anviksiki trayi varta
 danda-nitis tathaiva ca
evam vyahrtayas casan
 pranavo hy asya dahratah
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
The science of logical argument, the Vedic goals of life, and also law and order, moral codes and the celebrated hymns bhuh, bhuvah and svah all became manifested from the mouths of Brahma, and the pranava omkara was manifested from his heart.
Srimad Bhagavatam Canto 03, Chapter 12, Text 43
Srimad Bhagavatam Canto 03, Chapter 12, Text 45