Bhagavad Gita Chapter 17 Verse 23

Gita 17.23

ॐ, तत्, सत्, इति, निर्देशः, ब्रह्मणः, त्रिविधः, स्मृृतः,
ब्राह्मणाः, तेन, वेदाः, च, यज्ञाः, च, विहिताः, पुरा।।23।।

Gita 17.23

ॐ , Tat’, Sat’, iti, nirdeshH, brahmnH, trividhH, smrtH,
BraahmnaH, ten, vedaH, ch, yagyaaH, ch, vihitaH, pura ||23||

Translation: (ॐ) Om’ mantra of Brahm, (Tat’) Tat’ - this is coded mantra of ParBrahm, (Sat’) Sat’ - this is coded mantra of Purna Brahm (iti) in this way, this (trividhH) of three types (brahmnH) of rememberance of mantra of Purna Parmatma (nirdeshH) direction (smrtH) is said to be (ch) and (pura) in the beginning of nature (braahmnaH) the scholars (ten) that same (vedaH) based on Tatvgyan, Ved (ch) and (yagyaaH) yagya etc (vihitaH) created. (23)

Translation: ॐ/Om’ mantra of Brahm, Tat’ - this is coded mantra of ParBrahm, Sat’ - this is coded mantra of Purna Brahm. In this way, there is direction of rememberance of three types of mantras of Purna Parmatma, and in the beginning of nature, based on that very Tatvgyan, the scholars created Vedas and yagya etc. They used to worship according to that.