Śatapatha Brāhmaṇa ("of a hundred paths") 11.4.2.11

11.4.2.11

atha haitadantaḥśri yo'yaṃ saṃdhāyauṣṭhā uccaiḥ svaravadāśrāvayati śrīrvai svaro'ntarata eva tacriyaṃ dhatte'nnādo bhavati

And the inward-tending (antah-sri) one, indeed, it is when he closes his lips, and utters his call at a loud, toneful pitch: tone being prosperity, he thereby puts prosperity (srî) inside (antah) himself, and becomes an eater of food (rich).