Jaiminīya (Talavakāra) Brāhmaṇa 1.114

1.114

yo vā aṃśumekākṣaraṃ vedānnāda eva śreṣṭhassvānāṃ bhavati
atho saha eva tasyai janatāyā udgāyati
vāgvā aṃśurekākṣaraḥ
tadeva gāyatram
gāyatryai prastutāyai yadāderuttaramakṣaraṃ sa sthāṇuḥ
yastadudgāyannārabhate sthāṇumārabhate
ya enaṃ nirharati gāyatrīṃ chidrāṃ karoti
gāyatrīṃ chidrāṃ anu yajñassravati yajñamanu yajamāno yajamānamanu prajāḥ
sadhryaśvo ha smāha taigmāyudhiḥ ka u svidadya rasadihāvurasi nimradiṣyata
iti
ete ha vai rasadihau ye ete gāyatryā uttame akṣare
yaste udgāyannārabhate rasadihāvurasi nimardate
ya u ene nirharati gāyatrīṃ chidrāṃ karoti
gāyatrīṃ chidrāṃ anu yajñassravati yajñamanu yajamāno yajamānamanu prajāḥ

He who knows the one-syllable Aṃśu becomes an eater of food, preeminent among his own people; moreover, he sings the udgītha together for that community. Speech, indeed, is the one-syllable Aṃśu. That is the Gāyatra itself. When the Gāyatrī is sung in the prastāva, the syllable following the beginning is a post. He who, singing the udgītha, takes hold of it, takes hold of a post. He who removes it makes the Gāyatrī defective. Following the defective Gāyatrī, the sacrifice leaks; following the sacrifice, the sacrificer; following the sacrificer, the offspring. Sadhryaśva Taigmāyudhi used to say: "Who indeed today will crush upon his chest the two sap-milkers?" These two indeed are the two sap-milkers: the two final syllables of the Gāyatrī. He who, singing the udgītha, takes hold of them, crushes the two sap-milkers upon his chest. And he who removes them makes the Gāyatrī defective. Following the defective Gāyatrī, the sacrifice leaks; following the sacrifice, the sacrificer; following the sacrificer, the offspring.