Srimad Bhagavatam Canto 03, Chapter 12, Text 39

SB 3.12.39

itihasa-puranani
 pañcamam vedam isvarah
sarvebhya eva vaktrebhyah
 sasrje sarva-darsanah
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
Then he created the fifth Veda — the Puranas and the histories — from all his mouths, since he could see all the past, present and future.
 
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
There are histories of particular countries and nations and of the world, but the Puranas are the histories of the universe, not only in one millennium but in many kalpas. Brahma has knowledge of those historical facts, and therefore all the Puranas are histories. As originally composed by Brahma, they are part of the Vedas and are called the fifth Veda.
Srimad Bhagavatam Canto 03, Chapter 12, Text 38
Srimad Bhagavatam Canto 03, Chapter 12, Text 40