Mahabharata 13.109.4

उपवासः परं पुण्यमुपवासः परायणम्उपोष्येह नरश्रेष्ठ किं फलं प्रतिपद्यते

upavāsaḥ paraṃ puṇyamupavāsaḥ parāyaṇamupoṣyeha naraśreṣṭha kiṃ phalaṃ pratipadyate

Our plain-language meaning of this verse is waiting for scholar review.