B.G 18.25

अनुबन्धं क्षयं हिंसामनवेक्ष्य च पौरुषम्। मोहादारभ्यते कर्म यत्तत् तामसमुच्यते ॥२५॥

anubandhaṁ kṣayaṁ hiṁsāmanavekṣya ca pauruṣam। mohādārabhyate karma yattat tāmasamucyate ॥25॥

[अनुबन्धम् (anubandham) - consequence; क्षयम् (kṣayam) - destruction; हिंसाम् (hiṁsām) - violence; अनवेक्ष्य (anavekṣya) - without considering; च (ca) - and; पौरुषम् (pauruṣam) - effort; मोहात् (mohāt) - out of delusion; आरभ्यते (ārabhyate) - is undertaken; कर्म (karma) - action; यत् (yat) - which; तत् (tat) - that; तामसम् (tāmasam) - in the mode of ignorance; उच्यते (ucyate) - is said;]

The action that is undertaken out of delusion, without considering the consequences, destruction, violence, and effort, is said to be in the mode of 'tāmas', i.e. ignorance.