Bg 18.31

yayā dharmam adharmaṁ ca
kāryaṁ cākāryam eva ca
ayathāvat prajānāti
buddhiḥ sā pārtha rājasī
Synonyms: 
yayā — by which; dharmam — the principles of religion; adharmam — irreligion; ca — and; kāryam — what ought to be done; ca — also; akāryam — what ought not to be done; eva — certainly; ca — also; ayathā-vat — imperfectly; prajānāti — knows; buddhiḥ — intelligence; — that; pārtha — O son of Pṛthā; rājasī — in the mode of passion.
Translation: 
O son of Pṛthā, that understanding which cannot distinguish between religion and irreligion, between action that should be done and action that should not be done, is in the mode of passion.