B.G 18.31

यया धर्ममधर्मं च कार्यं चाकार्यमेव च। अयथावत् प्रजानाति बुद्धिः सा पार्थ राजसी ॥३१॥

yayā dharmamadharmaṃ ca kāryaṃ cākāryameva ca। ayathāvat prajānāti buddhiḥ sā pārtha rājasī ॥31॥

[यया (yayā) - by which; धर्मम् (dharmam) - righteousness; अधर्मं (adharmaṃ) - unrighteousness; च (ca) - and; कार्यं (kāryaṃ) - action; च (ca) - and; अकार्य (akārya) - inaction; मेव (meva) - indeed; च (ca) - and; अयथावत् (ayathāvat) - incorrectly; प्रजानाति (prajānāti) - perceives; बुद्धिः (buddhiḥ) - intellect; सा (sā) - that; पार्थ (pārtha) - O son of Pritha; राजसी (rājasī) - passionate;]

The intellect that perceives incorrectly righteousness as unrighteousness and action as inaction, O son of Pritha, is considered being of a passionate (rājasī) nature.