Mahabharata 13.26.36

माघमासं प्रयागे तु नियतः संशितव्रतःस्नात्वा तु भरतश्रेष्ठ निर्मलः स्वर्गमाप्नुयात्

māghamāsaṃ prayāge tu niyataḥ saṃśitavrataḥsnātvā tu bharataśreṣṭha nirmalaḥ svargamāpnuyāt

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