SB 3.8.9

provāca mahyaṁ sa dayālur ukto
 muniḥ pulastyena purāṇam ādyam
so ’haṁ tavaitat kathayāmi vatsa
 śraddhālave nityam anuvratāya
Word for word: 
provāca — said; mahyam — unto me; saḥ — he; dayāluḥ — kindhearted; uktaḥ — aforementioned; muniḥ — sage; pulastyena — by the sage Pulastya; purāṇam ādyam — the foremost of all the Purāṇas; saḥ aham — that also I; tava — unto you; etat — this; kathayāmi — shall speak; vatsa — my dear son; śraddhālave — unto one who is faithful; nityam — always; anuvratāya — unto one who is a follower.
Translation: 
The great sage Parāśara, as aforementioned, being so advised by the great sage Pulastya, spoke unto me the foremost of the Purāṇas [Bhāgavatam]. I shall also describe this before you, my dear son, in terms of my hearing, because you are always my faithful follower.
Purport: 

The great sage of the name Pulastya is the father of all demoniac descendants. Once upon a time Parāśara began a sacrifice in which all the demons were to be burnt to death because his father had been killed and devoured by one of them. The great sage Vasiṣṭha Muni arrived at the sacrifice and requested Parāśara to stop the deadly action, and because of Vasiṣṭha’s position and respect in the community of sages, Parāśara could not deny the request. Parāśara having stopped the sacrifice, Pulastya, the father of the demons, appreciated his brahminical temperament and gave the blessing that in the future he would be a great speaker on the Vedic literatures called the Purāṇas, the supplements of the Vedas. Parāśara’s action was appreciated by Pulastya because Parāśara had forgiven the demons out of his brahminical power of forgiveness. Parāśara was able to demolish all the demons in the sacrifice, but he considered, “Demons are so made that they devour living creatures, men and animals, but why on that account should I withdraw my brahminical qualification of forgiveness?” As the great speaker of the Purāṇas, Parāśara first of all spoke on the Śrīmad-Bhāgavata Purāṇa because it is the foremost of all the Purāṇas. Maitreya Muni desired to narrate the same Bhāgavatam be had heard from Parāśara, and Vidura was qualified to hear it because of his faithfulness and his following the instructions received from superiors. So Śrīmad-Bhāgavatam was being narrated from time immemorial by the disciplic succession, even before the time of Vyāsadeva. The so-called historians calculate the Purāṇas to be only a few hundred years old, but factually the Purāṇas existed from time immemorial, before all historical calculations by the mundaners and speculative philosophers.