SB 6.1.20

atra codāharantīmam
 itihāsaṁ purātanam
dūtānāṁ viṣṇu-yamayoḥ
 saṁvādas taṁ nibodha me
Synonyms: 
atra — in this connection; ca — also; udāharanti — they give as an example; imam — this; itihāsam — the history (of Ajāmila); purātanam — which is very old; dūtānām — of the order carriers; viṣṇu — of Lord Viṣṇu; yamayoḥ — and of Yamarāja; saṁvādaḥ — the discussion; tam — that; nibodha — try to understand; me — from me.
Translation: 
In this regard, learned scholars and saintly persons describe a very old historical incident involving a discussion between the order carriers of Lord Viṣṇu and those of Yamarāja. Please hear of this from me.
Purport: 

The Purāṇas, or old histories, are sometimes neglected by unintelligent men who consider their descriptions mythological. Actually, the descriptions of the Purāṇas, or the old histories of the universe, are factual, although not chronological. The Purāṇas record the chief incidents that have occurred over many millions of years, not only on this planet but also on other planets within the universe. Therefore all learned and realized Vedic scholars speak with references to the incidents in the Purāṇas. Śrīla Rūpa Gosvāmī accepts the Purāṇas to be as important as the Vedas themselves. Therefore in Bhakti-rasāmṛta-sindhu he quotes the following verse from the Brahma-yāmala:

śruti-smṛti-purāṇādi-
 pañcarātra-vidhiṁ vinā
aikāntikī harer bhaktir
 utpātāyaiva kalpate

“Devotional service of the Lord that ignores the authorized Vedic literatures like the Upaniṣads, Purāṇas and Nārada-pañcarātra is simply an unnecessary disturbance in society.” A devotee of Kṛṣṇa must refer not only to the Vedas, but also to the Purāṇas. One should not foolishly consider the Purāṇas mythological. If they were mythological, Śukadeva Gosvāmī would not have taken the trouble to recite the old historical incidents concerning the life of Ajāmila. Now the history begins as follows.