Jaiminīya (Talavakāra) Brāhmaṇa 2-3.88

He indeed becomes the vault and goes to the world of the vault who knows thus. He is indeed the vault who does not covet the world of another. Him he conquers with this. It is seventeen-versed. Prajāpati is seventeen-versed; Prajāpati is the vault, [thinking]: 'By the vault may we be vaults; by the vault may we go to the world of the vault.' It has both sāmans, the Bṛhat and the Rathantara. Neither of these alone is the vault; both of these indeed are the vault, [thinking]: 'By the vault may we be vaults; by the vault may we go to the world of the vault.' Its Ārbhava pavamāna or the Agniṣṭoma sāman is twenty-one-versed. Twelve months, five seasons, these three worlds, and yonder Āditya as the twenty-first. And he is indeed the vault of those gods who are below Prajāpati, [thinking]: 'By the vault may we be vaults; by the vault may we go to the world of the vault.' Arka of the gods in the highest vault, and the gods of the Arka in the highest vault are the two specified sāmans in the two pavamānas. They thus make the stoma prosperous by its proper form.

Now these two, the Udbhid and the Valabhid.

One desirous of propagation should sacrifice with these two.

There are nine-verse and fifteen-verse stomas, and seventeen-verse [stomas].

The deficient and the redundant are a couple leading to propagation.

Deficient is the one; redundant is the other.

From a couple, deficient and redundant, offspring and cattle are born.

Thus propagation is effected.

Therefore, one desirous of propagation should sacrifice with both.

Now they say: 'Only one desirous of spiritual luster should sacrifice with these two.'

Either of these amounts to six Gāyatrīs, and the other to six.

Brahman is the Gāyatrī.