Jaiminīya (Talavakāra) Brāhmaṇa 1.209

The night is indeed the Śarvarī. The gods said: 'A share has indeed come to us in the Śarvarī.' That is why the Apiśarvara [hymns] are called Apiśarvara. A share in the Śarvarī indeed comes to him who knows this. In the beginning, this [all] was with the Asuras. The gods, having conquered it, said: 'With what now shall we join day and night from above?' They saw this Rathantara Saṃdhi [sāman]. With it they joined day and night from above. Because they joined (samadadhuḥ), that is the nature of the Saṃdhi (saṃdhersaṃdhitvam). The Āśvina is indeed the recitation (uktha) of the Saṃdhi. They chant the praise with the Saṃdhi in the dead of night. The Āśvina [recitation] is recited until the rising of the sun, for the continuous connection of day and night, for the grasping together of day and night. The gods, having conquered day and night, made the vajra itself an enclosing-stick, for the protection of cattle, so that the Asuras would not approach. When these Uṣṇih verses are used at the end, the Uṣṇih is indeed a vajra; by means of the vajra he thus encloses the cattle, so that they may not be scattered away. His property is not scattered away, who knows this.

In the beginning, this was indeed with the Asuras.

The gods, having conquered it, said: 'Let us divide this amongst ourselves.'

They could not agree upon its division.

They said: 'Let us run a race for it.'

They ran a race.

Agni's chariot was first, then the Dawn's, then the Aśvins'.