Ṣaḍviṃśa Brāhmaṇa ("26th" book) 18.16

18.16

vāsiṣṭha vasiṣṭhagotrotpannaścaikitāneyo nāmatastadevāha sma | katham ? | sāma ha vai caturṛce gīyamānaṃ sāmaiva nūnam avaśyaṃ bhūyāṃsaṃ poṣaṃ puṣyati | taṃ sāmnaḥ poṣamanu yajamāno'pi poṣako bhavati | kiṃ ca caturthī adhyāsyā ṛk asāmnī tṛcāśritasāmarahiteti yat, etat vidhavā yā gatabhartṛkāyā janma
nirarthakamiva ityevameva ete caturṛce sāma gāyantaḥ śrotriyāḥ viduḥ jānanti iti | api ca yasmāccaturthyā tṛcānāśritaṃ sāmakaraṇaṃ vidhavājanmasadṛśaṃ tasmāt eteṣāṃ tṛce anyat adhyāsyāyām anyat sāma kurvatāṃ kule śrotriyāḥ śrutācārasaṃpannāḥ yuvānaśca santaḥ śatasaṃvatsaralakṣaṇāt āyuṣaḥ purā pūrvameva pramāyukā maraṇaśīlā bhavanti | ata eva teṣāṃ jāyā yuvatayaḥ satyaḥ vidhavā bhavanti | tatraiva hetupradarśanam | yat yasmāt tṛce'nyat sāma ekarce adhyāsyāyāmanyadbhavatīti | ato yadeva catasṛṣvṛkṣu ekaṃ sāma kriyate sa evātra vivakṣitaścaturṛcaḥ | itiśabdaścaikitāneyavākyasamāptyarthaḥ | etat caturṛce sāmagānaṃ pṛṣṭhyaṣaḍahasya tṛtīye ahni chandomānāmahnāṃ madhye dvayorhvoḥ mādhyaṃdinapavamāne veditavyam |
evaṃ caturṛce sāma vidhāya idānīmasminneva dvādaśāhe savanīyā ekādaśina āgneyakṛṣṇagrīvā ityādyāḥ paśavaḥ pratyaham ekaikaśa ālabhyante | uttame'hnāne ekaḥ paśuḥ ālabdhavyaḥ | sa kaḥ savanīya (kiṃsavanīya ?) ityapekṣāyāṃ vikalpenālabhyaṃ paśuṃ darśayituṃ prathamaṃ pakṣaṃ tāvadupan‍yasyati —