Shatapatha Brahmana 11.7.2.8

11.7.2.8

madhuko ha smāha paiṅgyaḥ visomena vā eke paśubandhena yajante sasomenaike divi vai soma āsīttaṃ gāyatrī vayo bhūtvāharattasya yatparṇamacidyata tatparṇasya parṇatvamiti nvā etadbrāhmaṇamudyate visomena vā eke paśubandhena yajante sasomenaike sa haiṣa visomena paśubandhena yajate yo'nyam pālāśādyūpaṃ kurute'tha haiṣa sasomena paśubandhena yajate yaḥ pālāśaṃ yūpaṃ kurute tasmātpālāśameva yūpaṃ kurvīta

Madhuka Paiṅgya once said, 'Some perform the animal sacrifice without Soma, and others do so with Soma. Now, Soma was in the heavens, and Gâyatrî, having become a bird, fetched him; and inasmuch as one of his leaves (parna) was cut off, that was how the Parna-tree arose:' such, indeed, is (the passage in) the Brâhmana that is told. And some, it is true, perform the animal sacrifice without Soma, and others with Soma; for he who makes the sacrificial stake other than of Palâsa wood, performs the animal sacrifice without Soma; and he who makes the sacrificial stake of Palâsa performs the animal sacrifice with Soma: therefore let him make his sacrificial stake of Palâsa wood.