oṁ tat sad iti nirdeśho brahmaṇas tri-vidhaḥ smṛitaḥ
brāhmaṇās tena vedāśh cha yajñāśh cha vihitāḥ purā||23||

Meaning : The sacred word “Om Tat Sat” is considered the symbol of Brahman (the Absolute Reality) in three forms. Through this word, the Vedas and the rituals of sacrifice were established long ago for the Brahmanas (priests and learned ones).