Śatapatha Brāhmaṇa ("of a hundred paths") 2.5.1.16

2.5.1.16

tasyām mithunamasti | yoṣā payasyā reto vājinaṃ tasmānmithunādviśvamasammitamanu prājāyata tadyadetasmānmithunādviśvamasammitamanu prājāyata tasmādvaiśvadevī bhavati

Therein a union takes place: the curdled milk (payasyâ, fem.) is female, and the whey is seed. From that union the infinite All was gradually generated; and since the infinite All was gradually generated from that union, therefore it (the offering of curds) belongs to the All-gods.