Śatapatha Brāhmaṇa ("of a hundred paths") 4.4.2.10

4.4.2.10

taṃ vā upāṃśupātreṇa gṛhṇāti | yadi sāvitramupāṃśupātreṇa gṛhṇīyādantaryāmapātreṇaitaṃ yadi sāvitramantaryāmapātreṇa gṛhṇīyādupāṃśupātreṇaitaṃ samānaṃ hyetadyadupāṃśvantaryāmau prāṇo hi yo vai prāṇaḥ sa udāno vṛṣā vai prāṇo yoṣā patnī mithunamevaitatprajananaṃ kriyate

He draws it with the Upâmsu vessel. If he draws the Sâvitra libation with the Upâmsu vessel, (he draws) this one with the Antaryâma vessel; and if he draws the Sâvitra with the Antaryâma vessel (he draws) this one with the Upâmsu vessel;--for one and the same indeed are the Upâmsu and Antaryâma, being breath, and that which is the out-breathing is also the in-breathing. Now the breath (prâna, masc.) is male, and the wife is female: a productive union is thus brought about.