Chapter 18 · verse 25 · gita.yoga.org

Bhagavad Gita 18.25

अनुबन्धं क्षयं हिंसामनपेक्ष्य च पौरुषम्।मोहादारभ्यते कर्म यत्तत्तामसमुच्यते

That action which is undertaken from delusion, without regard for the consequences, loss, injury, and one's own ability, is declared to be Tamasic (dark).