Manava Dharmashastra 5.36

5.36

prokṣaṇādayaḥ paśubandhe mantravantaḥ saṃskārā vihitāste yeṣāṃ kriyante paśūnāṃ vaidikayāgaśeṣāṇāṃ māṃsamadyāt | sītāyajñādiṣu ca satyapi sāmayācārikayāgaśeṣatve mantrasaṃskārābhāvādabhakṣyatā | śāśvatam | śāśvato nityo vaidika ityarthaḥ | āsthita āśritaḥ |

The Brāhmaṇa shall never eat animals that have not been consecrated with sacred texts; but those that have been consecrated with sacred texts, he shall eat, taking, his stand upon the eternal law.—(36)

Medhātithi’s commentary (manubhāṣya):
In connection with animals-sacrifice, ‘sprinkling with water’ and other consecrations have been laid down as to be done with sacred texts; and one shall eat the meat of those animals for whom all these have been performed, and which (thus) are the ‘remnants of sacrifices’ prescribed in the Vedas. But in the case of the and other sacrifices that are performed solely on the strength of usage (and for which there is no injunction in the Veda),—even though the meat would he the ‘remnant of sacrifice’, yet, since there would be no ‘consecration with sacred texts’, it would be ‘unfit for eating’.

‘Eternal’—Vedic.

‘Taking his stand’—dependent.—(36)