Chapter 17 · verse 23 · gita.yoga.org

Bhagavad Gita 17.23

तत्सदिति निर्देशो ब्रह्मणस्त्रिविधः स्मृतः।ब्राह्मणास्तेन वेदाश्च यज्ञाश्च विहिताः पुरा

"Om Tat Sat": This has been declared to be the triple designation of Brahman. By that, the Brahmanas, the Vedas, and the sacrifices were created formerly.