Bhagavad Gita Chapter 18, Verse 28

अयुक्तः प्राकृतः स्तब्धः शठो नैष्कृतिकोऽलसः | विषादी दीर्घसूत्री च कर्ता तामस उच्यते ||

ayuktaḥ prākṛtaḥ stabdhaḥ śaṭho naiṣkṛtiko 'lasaḥ viṣādī dīrgha-sūtrī ca kartā tāmasa ucyate

The doer who is unsteady, vulgar, stubborn, deceitful, malicious, lazy, despondent, and procrastinating, is called tamasic.

Krishna explains the tamasic doer. 'Ayuktaḥ prākṛtaḥ stabdhaḥ śaṭho naiṣkṛtiko 'lasaḥ'—unsteady (ayuktaḥ), vulgar (prākṛtaḥ), stubborn (stabdhaḥ), deceitful (śaṭhaḥ), malicious (naiṣkṛtikaḥ), lazy (alasḥ). 'Viṣādī dīrgha-sūtrī ca kartā tāmasa ucyate'—despondent (viṣādī), procrastinating (dīrgha-sūtrī), the doer (kartā) is called (ucyate) tamasic (tāmasaḥ). This is the tamasic doer: unsteady, uncultured, stubborn, deceitful, malicious, lazy, despondent, and procrastinating. This is the lowest kind of doer: driven by tamas (ignorance), which creates delusion, negligence, and harmful qualities. Unlike the sattvic doer (detached, balanced) and the rajasic doer (passionate, active), the tamasic doer is ignorant, lazy, and potentially harmful. This doer is bound by ignorance and negative qualities.