BṚHADĀRAṆYAKA UPANISHAD · 1.3.21
एष उ एव ब्रह्मणस्पतिः ।
वाग् वै ब्रह्म ।
तस्या एष पतिस् तस्माद् उ ब्रह्मणस्पतिः ॥
eṣa u eva brahmaṇaspatiḥ ।
vāg vai brahma ।
tasyā eṣa patis tasmād u brahmaṇaspatiḥ ॥
He (breath) is also Brahmanaspati, for speech is Brahman (Yagur-veda), and he is her lord; therefore he is Brahmanaspati.
F. Max Müller · The Upanishads, Sacred Books of the East 15 (1884)