Kauthumagrihyasutra 6

The joining of the fires of two wives. / Now then, among all varnas, if there is remarriage for brahmins: having previously brought forward half of the domestic fire, for the purpose of joining them together, on the fourth day, having begun in the evening, the patron of the sacrifice, having caused the previous fire to descend, making a sacrificial ground there, having established [it] with the triplet beginning 'agniṃ vo vṛdhantam', taking the next wife's [fire] in a vessel to the new fire, having joined [them] with the triplet beginning 'imaṃ stomam', at the end of each triplet [reciting] four syllables in a whisper; then, clarified butter having been offered with the six [verses] beginning 'agnir aitu', he should make the patron of the sacrifice recite [the formula]; having controlled the breath, having sprinkled around, [he offers:] 'To Agni svāhā! To Prajāpati svāhā!'; having sprinkled around again, having performed the internalisation of the sacred fire, having sung the Vāmadevya; if in another region, he should perform it there in a common fire; having joined it as before, if there is marriage with a non-preferred [or supplementary bride], there is a special rule there; we shall explain that: having invited brahmins, he should feed them a hundred cakes, or eight; having bathed and adorned himself, taking water with a water pot, going into another forest, looking for an arka branch endowed with these qualities in that place: un-withered, tender, having auspicious leaves, bearing fruit, broad, facing eastward, possessing [vitality]; for the sake of its father, having examined a brahmin who knows the Veda, having bathed [the branch], he should not carry away the arka branch; having covered it with a new garment, the brahmin gives the gift of the arka maiden [saying] 'devasya tvā...'; [the groom says] 'I receive the bridegroom's [gift]'; making a sacrificial ground in front, sitting to the north of the arka [branch], having surrounded the arka branch with eight brahmins, all facing east or facing north, the brahmin, having then worshipped the brahmin, should give ten cakes to each; placing the remainder to the north, having established a common fire, having then performed [the rites] from the sweeping up to the introductory formula, having offered the limb of the sacrificial firewood, having then offered with the three mystic utterances, with the six [verses] beginning 'agnir aitu', [and] again with the three [mystic utterances]; then the patron of the sacrifice, standing, taking circumambulation from left to right of the fire, Agni and Āditya, [with] internalisation of all brahmins, [and] externalisation of heaven and earth, should silently perform circumambulation three times; sitting down in his own place, he should take the companion with his right hand; he recites in a whisper 'tad gṛhṇāmi te...'; then, having completed the later offerings, he should give ten remaining cakes to the priest, [and] himself should eat ten; having sprinkled around the fire there, having worshipped it, he should offer clarified butter with the three mystic utterances; having discharged that, then the Vāmadevya, the words of blessing of the brahmins; he should go to the maiden's house; then remarriage, remarriage.

KauthGS 7: