Mahabharata 13.110.5

भीष्म उवाच · bhīṣma uvāca

इदमङ्गिरसा प्रोक्तमुपवासफलात्मकम्विधिं यज्ञफलैस्तुल्यं तन्निबोध युधिष्ठिर

idamaṅgirasā proktamupavāsaphalātmakamvidhiṃ yajñaphalaistulyaṃ tannibodha yudhiṣṭhira

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