Shatapatha Brahmana 8.3.4.11

8.3.4.11

athātaḥ saṃskṛtireva | yā amūrekādaśeṣṭakā upadadhāti yo 'sau prathamo 'nuvākastadantarikṣaṃ sa ātmā tadyattā ekādaśa bhavantyekādaśākṣarā vai triṣṭuptraiṣṭubhamantarikṣamatha yā uttarāḥ ṣaṣṭiḥ sa vāyuḥ sa prajāpatiḥ so 'gniḥ sa yajamānaḥ

Now as to the restoration (of Pragâpati-Agni). Those eleven bricks he lays down, which (constitute) that first anuvâka, are the air and this body (of Agni, the altar). And as to why there are eleven of these, it is because the Trishtubh consists of eleven syllables, and the air is of the trishtubh nature. And the sixty subsequent (bricks) are Vâyu, Pragâpati, Agni, the Sacrificer.