Srimad-Bhagavatam: Canto 1 - Chapter 1 - Verse 20
Sanskrit:
ऋग्यजु:सामाथर्वाख्या वेदाश्चत्वार उद्धृता: ।इतिहासपुराणं च पञ्चमो वेद उच्यते ॥ २० ॥
ITRANS:
ṛg-yajuḥ-sāmātharvākhyāvedāś catvāra uddhṛtāḥitihāsa-purāṇaṁ capañcamo veda ucyate
Translation:
The four divisions of the original sources of knowledge [the Vedas] were made separately. But the historical facts and authentic stories mentioned in the Purāṇas are called the fifth Veda.