Shatapatha Brahmana 6.6.1.13

6.6.1.13

tāni vai bhūyāṃsi bhavanti | agnicityāyāṃ yadu cānagnicityāyāṃ tasyākto bandhurubhayāni bhavanti tasyokto 'dhvarasya pūrvāṇyathāgnestasyo evoktaḥ

There are many of these, in the building of the fire-altar as well as at any other (special ceremony): the significance of this has been told. They are of both kinds: (the significance) of this has been told;--first those of the sacrifice, and then those of the fire: (the significance) of this also has been told.