Jaiminīya (Talavakāra) Brāhmaṇa 2.275

He indeed enters a divine assembly who sings the Udgītha with the Pavamānas.
Just as if approaching a superior, thus learning, as it were, imitating, as it were, bowing down, as it were, he should sing the Udgītha with perfected [chants], being capable and unimpeded.
Like welcoming one who approaches, like giving whatever one might ask—such is that.
Now, he who sings the Udgītha with these unperfected [chants], incapable and impeded, like turning away one who approaches, like not giving whatever one might ask—such is that.
And regarding this, right here the success and failure of the sacrifice are known.
A ford indeed is this, namely, the Pavamānas.
He who wades through a ford uncovered is smeared with mud or injured.
Now he who wades through covered is not smeared with mud, nor is he injured.
In this way indeed the Pavamānas are to be approached.
Regarding this they say, “Since the other stotras have stotriya-introductory verses, why then do the Pavamānas have no stotriya-introductory verses?”
He should say, “The Pavamānas are the vital breaths, and the Pāvamānī [verses] are the vital breaths.
So, if they were to begin the Pavamānas with Pāvamānī [verses], they would wipe away the vital breaths outward.”
Since they begin them with an Anuṣṭubh—speech indeed is the Anuṣṭubh, the downward breath is restrained in speech—by speech alone he thereby supports the downward breath.

Regarding this they say: “This stotra is unpacified, as it were, since they do not begin it with a stotriya [verse].

By what is it, among them, provided with a stotriya-introductory verse?”

He should say: “Speech indeed is the Anuṣṭubh; and in speech are all the meters.

Because the Pavamāna belongs to Agni and Indra, thereby it is, among them, provided with a stotriya-introductory verse.”