Whatever is read as said in the Vedas and in other scriptures is considered as authority. The authority, again, of the Vedas and other scriptures, is eternal.
प्रमाणं यत् स्ववेदोक्तं शास्त्रोक्तं यच्च पठ्यते। वेदशास्त्रद्वयं चैव प्रमाणं तत् सनातनम्॥