BṚHADĀRAṆYAKA UPANISHAD · 5.4.1

तद् वै तद् एतद् एव तद् आस ।
सत्यम् एव ।
स यो हैतं महद् यक्षं प्रथमजं वेद सत्यं ब्रह्मेति जयतीमांल् लोकान् -- जित इन् न्व् असाव् असत् -- य एवम् एतन् महद् यक्षं प्रथमजं वेद सत्यं ब्रह्मेति ।
सत्यं ह्य् एव ब्रह्म ॥

tad vai tad etad eva tad āsa ।
satyam eva ।
sa yo haitaṃ mahad yakṣaṃ prathamajaṃ veda satyaṃ brahmeti jayatīmāṃl lokān -- jita in nv asāv asat -- ya evam etan mahad yakṣaṃ prathamajaṃ veda satyaṃ brahmeti ।
satyaṃ hy eva brahma ॥

This (heart) indeed is even that, it was indeed the true (Brahman). And whosoever knows this great glorious first-born as the true Brahman, he conquers these worlds, and conquered likewise may that (enemy) be! yes, whosoever knows this great glorious first-born as the true Brahman; for Brahman is the true.

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