Śatapatha Brāhmaṇa ("of a hundred paths") 3.2.4.15

3.2.4.15

athāparaṃ caturgṛhītamājyaṃ gṛhītvā | anvārabhasva yajamānetyāhāporṇuvanti śālāyai dvāre dakṣiṇataḥ somakrayaṇyupatiṣṭhate tatprahitāmevaināmetatsatīm prāhaiṣīdvāgvai somakrayaṇī nidānena tāmetayāhutyāpraiṣītprītayā somaṃ krīṇānīti

Having then taken butter a second time in four parts, he says, 'Sacrificer, hold on behind!' They open the (south and east) doors of the hall (and walk out). On the right side (of the front door) approaches the Soma-cow: (by having) her thus put forward, he has sent her forth (to Soma); for the Soma-cow is in reality Vâk: it is her he has gratified by this offering, thinking, 'With her, when gratified, I will buy Soma.'