Taittiriyaka-Upanishad: Second Valli, Fourth Anuvaka
“He who knows the bliss of that Brahman, from whence all speech, with the mind, turns away unable to reach it, he never fears.” The embodied Self of this (consisting of mind) is the same as that of the former (consisting of breath).
Different from this, which consists of mind, is the other, the inner Self, which consists of understanding. 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. Faith is its head. What is right is its right arm. What is true is its left arm. Absorption (yoga) is its trunk. The great (intellect?) is the seat (the support).
On this there is also the following Sloka: