śraddhātrayavibhāgayoga - Verse śloka 23
śloka 23
oṃtatsaditi nirdeśo brahmaṇastrividhaḥ smṛtaḥ |
brāhmaṇāstena vedāśca yajñāśca vihitāḥ purā ||17-23||
Translation
'Om, Tat, Sat'—thus is this threefold designation (name) of Brahman spoken; from that alone did Brahman, the Vedas and sacrifice originate in the beginning.