Śatapatha Brāhmaṇa ("of a hundred paths") 4.4.2.18

4.4.2.18

yadyukthyaḥ syāt | somam prabhāvayeti brūyātsa bibhradevaitatpātramagnīnneṣṭurupasthamāsīdatyagnirvā eṣa nidānena yadāgnīdhro yoṣā neṣṭā vṛṣā vā agnīdyoṣā neṣṭā mithunamevaitatprajananaṃ kriyata udānayati neṣṭā patnīṃ tāmudgātrā saṃkhyāpayati prajāpatirvṛṣāsi retodhā reto mayi dhehīti prajāpatirvā udgātā yoṣā patnī mithunamevaitatprajananaṃ kriyate

But if it be an Ukthya, let him say, 'Lengthen out the Soma!'--Holding the same vessel (from which the Pâtnîvata libation was made, the Agnîdh) sits down in the Neshtri's lap,--for he, the Agnîdh, is in reality Agni, and the Neshtri is female: the Agnîdh is male, and the Neshtri female,--a productive union is thus brought about. The Neshtri leads up the lady and makes her exchange looks with the Udgâtri, with 'Thou art Pragâpati, the male, the bestower of seed: lay thou seed into me!' The Udgâtri is Pragâpati, and the lady is a woman: a productive union is thus brought about.