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 oṁ; yat - that which; proktam - has been spoken; yat - that which is; na - not preceded by oṁ; 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.