Mahabharata — Anushasana Parva, Shloka 13
अत्रेः तपोबलप्रकाशः तथा च्यवनस्य सोमाधिकारः
Atri’s Illumination by Tapas; Cyavana and Soma-Entitlement
न च संध्यामुपासीत न च जाप्य॑ प्रवर्तयेत् । न संकिरेत् तदन्नं च ततः पूर्येत ब्राह्मण:
na ca sandhyām upāsīta na ca jāpyam pravartayet | na saṅkīret tad-annaṃ ca tataḥ pūryeta brāhmaṇaḥ ||
Bhīṣma said: “On the day a brāhmaṇa partakes of the food offered in a śrāddha, he should not perform the sandhyā worship, should not set in motion the recitation of japa (such as the Gāyatrī), and should not eat again. By observing these restraints, the brāhmaṇa’s ritual purity is duly restored and maintained.”
भीष्य उवाच
Educational Q&A
A brāhmaṇa who eats the śrāddha meal should observe specific restraints that day—refraining from sandhyā worship, from initiating mantra-japa (e.g., Gāyatrī), and from eating again—so that ritual purity and propriety connected with the śrāddha are preserved.
In the Anuśāsana Parva’s instruction on dharma, Bhīṣma is laying down detailed rules of conduct related to śrāddha observances, specifying what a brāhmaṇa participant should avoid on the day he partakes of the śrāddha offering.