CHĀNDOGYA UPANISHAD · 3.18.3

वाग् एव ब्रह्मणश् चतुर्थः पादः ।
सो ऽग्निना ज्योतिषा भाति च तपति च ।
भाति च तपति च कीर्त्या यशसा ब्रह्मवर्चसेन य एवं वेद ॥

vāg eva brahmaṇaś caturthaḥ pādaḥ ।
so ’gninā jyotiṣā bhāti ca tapati ca ।
bhāti ca tapati ca kīrtyā yaśasā brahmavarcasena ya evaṃ veda ॥

Speech is indeed the fourth foot of Brahman. That foot shines with Agni (fire) as its light, and warms. He who knows this, shines and warms through his celebrity, fame, and glory of countenance.

F. Max Müller · The Upanishads, Sacred Books of the East 1 (1879)