Verse
अयुक्तः प्राकृतः स्तब्धः शठो नैष्कृतिकोऽलसः ।विषादी दीर्घसूत्री च कर्ता तामस उच्यते ॥
One who acts with a mechanical mind (who does not put himself really into the work), is stupid, obstinate, cunning, insolent, lazy, easily depressed, procrastinating, that doer is called tamasic.
Gītā 18·28