Matsyapurana 142.47

142.47

ṛco yajūṃṣi sāmāni mantrāścātharvaṇāstu ye
saptarṣibhiśca ye proktāḥ smārtaṃ tu manurabravīt //

The Sapta rıṣis enunciated the Ṛig Yajuh Sâma and Atharvana mantras very accurately, and the sage Manu similarly dealt with his Smriti. In the Tretayuga the four Vedas, the bridge of dharma were all embodied in one. In the Dvâparayuga owing to the short life and intellect of men the Vedas were divided into four separate treatises. In days of yore the Ṛiṣis by virtue of their tapas could study the entire Vedas in one day and night. The Vedas taught the duties of the people in each yuga. In ancient days Svayambhu Brahmâ gave out the divine immortal Vedas with various Aṅgas and containing the Svadharmas pertaining to every yuga. Under the influence of Time by and by, the dharmas deviated from the Vedas and became perverted.—47-49.