सत्यमोमिति यत् प्रोक्तं यन्नेत्याहानृतं हि तत् ॥ ३८ ॥
śṛṇu me ’sura-sattama
satyam om iti yat proktaṁ
yan nety āhānṛtaṁ hi tat
atra api — in this regard also (in deciding what is truth and what is not truth); bahu-ṛcaiḥ — by the śruti-mantras known as Bahvṛca-śruti, which are evidence from the Vedas; gītam — what has been spoken; śṛṇu — just hear; me — from me; asura-sattama — O best of the asuras; satyam — the truth is; om iti — preceded by the word om; yat — that which; proktam — has been spoken; yat — that which is; na — not preceded by om; iti — thus; āha — it is said; anṛtam — untruth; hi — indeed; tat — that.
One might argue that since you have already promised, how can you refuse? O best of the demons, just take from me the evidence of the Bahvṛca-śruti, which says that a promise is truthful preceded by the word om and untruthful if not.