Jaiminīya (Talavakāra) Brāhmaṇa 1.225

1.225

yajñastanau vā ete sāmanī
etābhyāṃ vā indro yajñaṃ sarvānkāmānadugdha
duhe ha vai yajñaṃ sarvānkāmānya evaṃ veda
yajurnidhanaṃ vā etayoranyataratsāmanidhanamanyatarat
tadyadghṛtaścunnidhanaṃ tadyajurnidhanamatha yanmadhuścunnidhanaṃ tatsāmanidhanam
yā yajuṣaśca sāmnaścardhirṛdhnoti tāmṛddhimāpnoti tānkāmānya evaṃ veda
tadāhuryadājyena divā carantyatha kenaiṣāṃ rātrirājyavatī bhavatīti
ghṛtaścunnidhaneneti brūyāt
etena ha vai rātrirājyavatī bhavati
yadu ghṛtaścucca madhuścuccāṅgirasāvapaśyatāṃ tasmādevamākhyāyate

These two sāmans are the two breasts of the sacrifice.
With these two Indra milked all desires from the sacrifice.
He milks all desires from the sacrifice, who knows thus.
One of these two has a yajus-finale; the other has a sāman-finale.
That which has ghṛtaścut as finale has a yajus-finale; and that which has madhuścut as finale has a sāman-finale.
Whatever prosperity belongs to the yajus and to the sāman, that prosperity he prospers with, those desires he obtains, who knows thus.
They say about this: 'Since they perform [rites] by day with butter, by what does their night become possessed of butter?'
He should say: 'By having ghṛtaścut as finale.'
By this indeed the night becomes possessed of butter.
And because Ghṛtaścut and Madhuścut, the two Āṅgirases, saw them, therefore it is so called.