BṚHADĀRAṆYAKA UPANISHAD · 1.3.20

एष उ एव बृहस्पतिः ।
वाग् वै बृहती ।
तस्या एष पतिस् तस्माद् उ बृहस्पतिः ॥

eṣa u eva bṛhaspatiḥ ।
vāg vai bṛhatī ।
tasyā eṣa patis tasmād u bṛhaspatiḥ ॥

He (breath) is also Brihaspati, for speech is Brihatî (Rig-veda), and he is her lord; therefore he is Brihaspati.

F. Max Müller · The Upanishads, Sacred Books of the East 15 (1884)