Bhagavad Gita 17.23

तत्सदिति निर्देशो ब्रह्मणस्त्रिविधः स्मृतः।ब्राह्मणास्तेन वेदाश्च यज्ञाश्च विहिताः पुरा॥

tatsaditi nirdeśo brahmaṇastrividhaḥ smṛtaḥ |brāhmaṇāstena vedāśca yajñāśca vihitāḥ purā ||

"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.

Om Tat Sat is the triple designation of the Eternal Spirit, by which the Vedic Scriptures, ceremonials, and sacrifices were ordained of old.

Our plain-language meaning of this verse is waiting for scholar review.