Śatapatha Brāhmaṇa ("of a hundred paths") 1.8.3.27

1.8.3.27

yujau ha vā ete yajñasya yatsrucau | te etadyuṅkte yatpracarati sa yaṃ nidhāyāvadyedyathā vāhanamavārcevaṃ tatte etatsviṣṭakṛti vimocanamāgacataste tatsādayati tadvimuñcati te etatpunaḥ prayuṅkte 'nuyājeṣu so 'nuyājaiścaritvaitadvimocanamāgacati te tatsādayati tadvimuñcati te etatpunaḥ prayuṅkte yatsampragṛhṇāti tadyāṃ gatimabhiyuṅkte tāṃ gatiṃ gatvā vimuñcate yajñaṃ vā anu prajāstasmādayam puruṣo yuṅkte 'tha vimuñcate 'tha yuṅkte tadyāṃ gatimabhiyuṅkte tāṃ gatiṃ gatvāntato vimuñcate sa sādayati ghṛtācī stho dhuryau pātaṃsumne sthaḥ sumne mā dhattamiti sādhvyau sthaḥ sādhau mā dhattamityevaitadāha

Yoke-fellows, indeed, are these two spoons for the sacrifice: he yokes them when he starts (or, first uses them). Now, were he only to release (unyoke) either of them after putting it down, it would fall down just as a draught animal (would, if made to lie down before being unyoked). At the Svishtakrit these two undergo an unyoking: he then lays them down, and so unyokes them. He then yokes them again, at the after-offerings. Having performed the after-offerings, he effects another unyoking: he lays them down, and so unyokes them. Thereupon he yokes them again when he seizes them both at the same time; and when he has travelled over the way for which he has yoked them, he unyokes them. After the sacrifice offspring (is produced). Hence this man yokes (unites), and then unyokes, and again yokes them; and when he has travelled over the way for which he yoked them, he finally unyokes them. He lays (the spoons) down, with the text (Vâg. S. II, 19 a), 'Fond of butter are ye; protect the two yoke-fellows! gracious are ye: lead me to grace!' whereby he says, 'good are ye: lead me to goodness!'