Taittiriyaka-Upanishad: Second Valli, Third Anuvaka
The Devas breathe after breath (prâna), so do men and cattle. Breath is the life of beings, therefore it is called sarvayusha (all-enlivening).
They who worship breath as Brahman, obtain the full life. For breath is the life of all beings, and therefore it is called sarvayusha. The embodied Self of this (consisting of breath) is the same as that of the former (consisting of food).
Different from this, which consists of breath, is the other, the inner Self, which consists of mind. The former is filled by this. It also has the shape of man. Like the human shape of the former is the human shape of the latter. Yagus is its head. Rik is its right arm. Saman is its left arm. The doctrine (adesa, i.e. the Brahmana) is its trunk. The Athar-vangiras (Atharva-hymns) the seat (the support).
On this there is also the following Sloka: