चतुर्युगाख्यान (Caturyuga-Ākhyāna) — Yuga-wise Origins and Measurements of Beings
अथर्वगर्यजुषां साम्नां वेदेष्विह पृथक्पृथक् / ऋषीणां तप्यतामुग्रं तपः परमदुष्करम्
atharvagaryajuṣāṃ sāmnāṃ vedeṣviha pṛthakpṛthak / ṛṣīṇāṃ tapyatāmugraṃ tapaḥ paramaduṣkaram
Here within the Vedas, Atharva, Ṛg, Yajus, and Sāman stand each apart; and the fierce tapas of the rishis who endure it is supremely hard to perform.