Śatapatha Brāhmaṇa ("of a hundred paths") 4.4.2.15

4.4.2.15

athāhāgnītpātnīvatasya yajeti | vṛṣā vā agnīdyoṣā patnī mithunamevaitatprajananaṃ kriyate sa juhotyagnā i patnīvnniti vṛṣā vā agniryoṣā patnī mithunamevaitatprajananaṃ kriyate

He then says, 'Agnîdh, pronounce the offering prayer of the Pâtnîvata!' The Agnîdh is male, and the wife is female: thus a productive union is brought about. He offers with (Vâg. S. VIII, 10), 'O Agni, wife-leader!'--Agni is male, and the wife is female: thus a productive union is brought about.