Shatapatha Brahmana 13.3.6.6

13.3.6.6

dvādaśa brahmaudanānutthāya nirvapati dvādaśabhirveṣṭibhiryajate tadāhuryajñasya vā etadrūpaṃ yadiṣṭayo yadiṣṭibhiryajetopanāmuka enaṃ yajñaḥ syātpāpīyāṃstu syādyātayāmāni vā etadījānasya candāṃsi bhavanti tāni kimetāvadāśu prayuñjīta sarvā vai saṃsthite yajñe vāgāpyate sātrāptā yātayāmnī bhavati krūrīkṛteva hi bhavatyaruṣkṛtā vāgvai yajñastasmānna prayuñjīteti

Having stepped out (of the water) he prepares twelve messes of cooked rice for the priests, or performs twelve ishtis. Concerning this they say, 'These to wit, ishtis--are a form of sacrifice: were he to perform ishtis, the sacrifice would be ready to incline towards him; but he would become the worse for it, for, surely, of exhausted strength now are the metres (offering formulas) of him who has performed the Soma-sacrifice;--how could he make use of them so soon? For when the sacrifice is complete, Vâk (speech and sacred writ) is wholly gained, and, being gained, it now is exhausted in strength, and, as it were, wounded and mangled; but sacrifice is speech: hence he should not make use of it.'