Bhagavad Gita · 17.23

ॐ तत्सदिति निर्देशो ब्रह्मणस्त्रिविधः स्मृतः।ब्राह्मणास्तेन वेदाश्च यज्ञाश्च विहिताः पुरा॥

oṁ tat sad iti nirdeśho brahmaṇas trividhaḥ smṛitaḥ brāhmaṇās tena vedāśh cha yajñāśh cha vihitāḥ purā

Om Tat Sat — this has been declared as the threefold designation of Brahman. By this, the Brahmanas, the Vedas, and sacrifices were ordained in ancient times.

— Bhagavad Gita 17.23

Source: Sacred-Texts.com (Sanskrit) + Bhagavad-Gita.io (translations)